AEE Ameren Corp

Notes to Financial Statements

December 31, 2015 and 2014

General

The following is a summary of the various provisions of the Ameren Corporation Savings Investment Plan (the “Plan”). Participants should refer to the Plan document for more complete information.

The Plan is a defined contribution plan. Its purpose is to provide employees eligible to participate (the “Participants”) of Ameren Corporation (the “Company”) and its wholly owned subsidiaries the option to defer a portion of their compensation for federal income tax purposes in accordance with Section 401(k) of the Internal Revenue Code (the “Code”). The Plan is subject to certain provisions of the Employee Retirement Income Security Act of 1974 (“ERISA”), as amended, and regulations of the Securities and Exchange Commission.

The Company serves as sponsor of the Plan, and, consequently, has the authority to amend or terminate the Plan subject to certain restrictions. The Board of Directors of the Company has the authority and responsibility for the general administration of the Plan. Fidelity Management Trust Company, as Trustee, has the authority and responsibility to hold and protect the assets of the Plan in accordance with Plan provisions and with the Trust and Administrative Agreement.

Participation

All regular full-time employees are eligible to participate upon employment, and part-time or temporary employees are eligible to participate upon completion of a year of service of at least 1,000 hours. Employees covered by a collective bargaining agreement (“CBA”) are eligible to participate only if the CBA provides for such participation.

If employees do not make an election, nor opt-out within 30 days of employment; they are automatically enrolled at a 6% pre-tax contribution rate, invested in a Target Date fund based upon the date at which the participant is or will be age 65, and further enrolled in auto-escalation increasing their pre-tax contribution 1% annually, with no cap on the annual increases. Employees may opt-out or make alternative elections at any time.

Contributions

Each year, Participants may contribute up to 100% of eligible compensation, as defined in the Plan, and subject to annual limitations imposed by the Code.

The Company makes an Employer Basic Matching Contribution plus an Employer Additional Matching Contribution in an amount equal to a percent of the amount each Participant contributes to the Plan, up to a certain maximum percentage of the Participant’s compensation that he or she elects to contribute to the Plan each year. The amount of Company matching contribution depends on the Participant’s employment classification, and for contract employees is determined by the collective bargaining agreement with the specific union representing the Participants. The Company also makes true-up Employer Basic Matching Contributions for Participants who contribute the IRS maximum before the end of the year and, as a result, do not receive the full company match. The Employer Additional Matching Contributions are invested in the Ameren Stock Fund.

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Ameren Corporation

Savings Investment Plan

Notes to Financial Statements

December 31, 2015 and 2014

The Plan permits “catch-up” contributions for all employees age 50 and older. Eligible employees could contribute $6,000 and $5,500 in 2015 and 2014, respectively, as a “catch-up” contribution. The Company does not match “catch-up” contributions.

Participants direct the investment of their contributions and the Employer Basic Matching Contributions to his or her account to any of the investment options available under the Plan, including Company stock. Contributions may be allocated to a single investment option or allocated in increments of one percent to any combination of investment options. Such elections may be changed daily.

Earnings derived from the assets of any investment fund are reinvested in the fund to which they relate. Participants may elect daily to reallocate, by actual dollar or percentage in one percent increments, the value of their accounts between funds. Pending investment of the assets into any investment fund, the Trustee may temporarily make certain short-term investments.

Participant Accounts

Each Participant’s account is credited with the Participant’s contributions and an allocation of (a) the Company’s contributions, and (b) Plan earnings, and is charged with an allocation of administrative expenses. Allocations are based on Participant contributions, eligible compensation, Participant account balances, or specific Participant transactions, as defined. The benefit to which the Participant is entitled is the benefit which can be provided from the Participant’s account. Each Participant directs the investment of his or her account to any of the investment options available under the Plan.

Notes Receivable from Participants

The Plan permits Participants to borrow from their accounts within the Plan. Such borrowings may be made subject to the following: (1) the minimum amount of the loan is $1,000, (2) the amount of the loan may not exceed the lesser of $50,000 or 50% of the vested amount in the Participant’s account, (3) the loan will bear a fixed interest rate and repayments will be made through mutual agreement subject to certain statutory repayment time limits, (4) each loan shall bear a reasonable interest rate as determined under policies established for the Plan and (5) such other rules and regulations as may be adopted by the Company. At December 31, 2015 and 2014, the interest rates on participant loans ranged from 4.00 percent to 10.50 percent.

Vesting

The amounts in Participants’ accounts, including Company contributions, are fully vested at all times.

Payment of Benefits

The total amount of a Participant’s account shall be distributed to the Participant according to one of the options as described in the Plan document and as elected by the Participant after termination of employment. All distributions shall be in the form of cash except that Participants may elect to have his or her interest in the Ameren Stock Fund distributed in shares of Ameren common stock. Participants may withdraw certain basic contributions, rollover contributions and related earnings thereon upon reaching age 59 1/2, in the event of total disability or financial hardship as defined by the Plan or the Code. For purposes of distributions, the Participant’s account value will be determined as of the last business day coincident with or immediately preceding the day of distribution. Contributions to the Plan and investment income thereon are taxable to Participants upon distribution pursuant to the rules provided for under the Plan and the Code.

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Ameren Corporation

Savings Investment Plan

Notes to Financial Statements

December 31, 2015 and 2014

The Plan also allows, at the discretion of the Company, participants of the former Union Electric Company Employee Stock Ownership Plan and the former Ameren Corporation Employee Stock Ownership Plan for Certain Employees of AmerenCIPS, to receive certain distributions prior to termination of employment.

Plan Termination

The Company intends to continue the Plan indefinitely. However, the Company may at any time and for any reason, subject to ERISA and Internal Revenue Service regulations, suspend or terminate the Plan provided that such action does not retroactively adversely affect the rights of any Participant under the Plan.

Basis of Accounting

The accompanying financial statements of the Plan are prepared on the accrual basis of accounting, except that benefit payments to Participants are recorded upon distribution.

Use of Estimates

The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of changes in net assets available for benefits during the reporting period. Actual results could differ from those estimates.

Investment Valuation and Income Recognition

All investments are presented at fair value, except for fully benefit-responsive investment contracts, which are reported at contract value, as of December 31, 2015 and 2014. Fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. See Note 3 for discussion of fair value measurements.

The Plan has direct investments in fully benefit-responsive investment contracts. Investments held by a defined contribution plan are required to be reported at fair value, except for fully benefit-responsive investment contracts. Contract value is the relevant measurement attribute for the portion of the net assets available for benefits of a defined contribution plan attributable to fully benefit-responsive investment contracts because contract value is the amount Participants normally would receive if they were to initiate permitted transactions under the terms of the Plan. Contract value represents contributions made under each contract, plus earnings, less participant withdrawals and administrative expenses.

Purchases and sales of securities are recorded on a trade date basis. Interest income is recorded on the accrual basis. Dividend income is recorded on the ex-dividend date. Net appreciation (depreciation) in fair value of investments includes the Plan’s gains and losses on investments bought and sold as well as held during the year.

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Ameren Corporation

Savings Investment Plan

Notes to Financial Statements

December 31, 2015 and 2014

Notes Receivable from Participants

Notes receivable from Participants are measured at their unpaid principal balance plus any accrued but unpaid interest, with no allowance for credit losses, as repayments of principal and interest are received through payroll deductions and the notes are collateralized by the Participants’ account balances. Delinquent participant loans are reclassified as distributions based upon the terms of the Plan document.

Administrative Expenses

Fees associated with administering the Plan are generally paid by the Plan. Through March 31, 2015, Trustee and recordkeeping fees were primarily paid via (1) revenue sharing payments (payments made directly from investment managers to the recordkeeper), (2) fees accrued in the investment funds that do not pay revenue sharing, and (3) flat dollar fees that are assessed to all Participants quarterly. Beginning April 1, 2015, Trustee and recordkeeping fees are primarily paid via flat dollar fees that are assessed to all Participants quarterly. Also, effective April 1, 2015, revenue sharing payments are allocated to Participant accounts quarterly.

Risks and Uncertainties

Investment securities are exposed to various risks, such as interest rate, market and credit. Due to the level of risk associated with certain investment securities and the level of uncertainty related to changes in the value of investment securities, it is at least reasonably possible that changes in risks in the near term could materially affect the Participants’ account balances and the amounts reported in the Statement of Net Assets Available for Benefits.

Concentrations

Company common stock comprised 12% of investments at December 31, 2015 and December 31, 2014.

New Accounting Standards

In May 2015, the Financial Accounting Standards Board issued ASU 2015-07, Fair Value Measurement (Topic 820:   Disclosures for Investments in Certain Entities that Calculate Net Asset Value Per Share (or Its Equivalent).   Under this guidance, investments measured at net asset value (“NAV”), under the existing practical expedient provided under ASC topic 820, are excluded from the fair value hierarchy. The guidance requires reporting entities to reconcile the fair value hierarchy disclosure to the statement of net assets available for benefits by disclosing the amount of investments measured using the practical expedient. The ASU is effective for fiscal years beginning after December 15, 2016 (December 15, 2015 for public business entities), with early adoption permitted. Retrospective application is required. Management is currently assessing the impacts of this guidance on the Plan’s disclosures.

In July 2015, the Financial Accounting Standards Board issued ASU 2015-12, Plan Accounting:   Defined Benefit Pension Plans (Topic 960), Defined Contribution Pension Plans (Topic 962), Health and Welfare Benefit Plans (Topic 965):   (Part I) Fully Benefit-Responsive Investment Contracts, (Part II) Plan Investment Disclosures, (Part III) Measurement Date Practical Expedient.   Part I eliminates the requirements to measure the fair value of fully benefit-responsive investment contracts and provide certain disclosures. Contract value is the only required measure for fully benefit-responsive investment contracts. Thus, on the statements of net assets available for benefits at December 31, 2014, investments at fair value was reduced by the previously

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Ameren Corporation

Savings Investment Plan

Notes to Financial Statements

December 31, 2015 and 2014

reported fair value of the fully-benefit responsive investment contracts, $271,318,703, and the adjustment from fair value to contract value for fully benefit-responsive investment contracts of $(671,952) was eliminated; the net of these adjustments resulted in recording $270,646,751 of investments at contract value at December 31, 2014. Also, Note 3 Fair Value Measurements at December 31, 2014 now excludes the previously reported fair value of the fully benefit-responsive investment contracts, $271,318,703. Part II eliminates the requirements to disclose individual investments that represent 5 percent or more of net assets available for benefits and the net appreciation or depreciation in fair value of investment by general type. Part II also simplifies the level of disaggregation of investments that are measured using fair value. Plans will continue to disaggregate investment that are measured using fair value by general type; however, plans are no longer required to disaggregate investments by nature, characteristics and risks. Further, the disclosure of information about fair value measurements shall be provided by general type of plan asset. Part III is not applicable to the Plan. The ASU is effective for fiscal years beginning after December 15, 2015, with early adoption permitted. Parts I and II are to be applied retrospectively. Management has elected to adopt Parts I and II early. The adoption of this standard had no effect on the Plan’s net assets available for benefits or changes therein.

The authoritative guidance issued by the FASB regarding fair value measurement provides a framework for measuring fair value for all assets and liabilities that are measured and reported at fair value. The guidance defines fair value as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Certain assumptions that market participants would use in pricing the asset or liability, including assumptions about risk or the risks inherent in the inputs to the valuation, were used in the valuation process. Inputs to valuation can be readily observable, market corroborated, or unobservable. Valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs were used. The provisions also establish a fair value hierarchy that prioritizes the inputs used to measure fair value. All financial assets and liabilities carried at fair value were classified in one of the following three hierarchy levels:

Level 1: Inputs based on quoted prices in active markets for identical assets or liabilities that the Plan has the ability to access at the reporting date.

Level 2: Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. Inputs to the valuation methodology include:

Level 3: Inputs to the valuation methodology that are unobservable and significant to the fair value measurement.

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Ameren Corporation

Savings Investment Plan

Notes to Financial Statements

December 31, 2015 and 2014

The asset or liability’s fair value measurement level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

Following is a description of the valuation methodologies used for assets measured at fair value.

There have been no changes in the methodologies used during 2015.

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Ameren Corporation

Savings Investment Plan

Notes to Financial Statements

December 31, 2015 and 2014

The following table sets forth, by level within the fair value hierarchy, Plan assets measured at fair value on a recurring basis as of December 31, 2015:

The following table sets forth, by level within the fair value hierarchy, Plan assets measured at fair value on a recurring basis as of December 31, 2014:

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Ameren Corporation

Savings Investment Plan

Notes to Financial Statements

December 31, 2015 and 2014

The Plan does not hold any investments requiring Level 3 measurements, and there have not been any transfers between measurement input levels in 2015 or 2014.

In February 2014, the Plan invested in a stable value account that is separately managed by Galliard Capital Management. The separately-managed account holds (1) an investment in a money market mutual fund, and (2) a portfolio of synthetic investment contracts, valued at $283,716,698 and $270,646,751 at December 31, 2015 and December 31, 2014, respectively. The investment contracts meet the fully benefit-responsive investment criteria and therefore are reported at contract value. Contract value is the relevant measure for fully benefit-responsive investment contracts because this is the amount received by Participants if they were to initiate permitted transactions under the terms of the Plan. Contract value represents contributions made under each contract, plus earnings, less participant withdrawals and administrative expenses.

The investment contracts are issued by the following insurance companies:

The underlying investments of the AGL, Prudential, and NYL contracts are holdings in collective trust funds. The underlying investments of the Mass Mutual and Met Life contracts are holdings in portfolios of fixed income securities, which are segregated from the insurance company’s general account assets. The segregation of these assets from the insurance company’s general account offers certain protections to mitigate the risk that these assets might be subject to creditor claims other than those of the separate account GIC owners.

The investment contracts include wrapper contracts, which are agreements for the wrap issuer to make payments to the Plan in certain circumstances. The wrapper contract typically includes certain conditions and limitations on the underlying assets owned by the Plan. The contracts are designed to accrue interest based on crediting rates established by the contract issuers, and also provide a guarantee that the credit rate will not fall below zero percent. Cash flow volatility (for example, timing of benefit payments) as well as asset underperformance can be passed through to the Plan through adjustments to future contract crediting rates. Formulas are provided in each contract that adjusts renewal crediting rates to recognize the difference between the fair value and the book value of the underlying assets. Crediting rates are reset at least quarterly.

The Plan’s ability to receive amounts due in accordance with fully benefit-responsive investment contracts is dependent on the third-party issuer’s ability to meet its financial obligations. The issuer’s ability to meet its contractual obligations may be affected by future economic and regulatory developments.

Certain events might limit the ability of the Plan to transact at contract value. Investment contracts generally provide for withdrawals associated with certain events which are not in the ordinary

11

Ameren Corporation

Savings Investment Plan

Notes to Financial Statements

December 31, 2015 and 2014

course of operations. These withdrawals are paid with a market value adjustment applied to the withdrawal as defined in the investment contract. Each contract issuer specifies the events which may trigger a market value adjustment; however, such events may include all or a portion of the following:

No events are probable of occurring that might limit the ability of the Plan to transact at contract value with the contract issuers and that also would limit the ability of the Plan to transact at contract value with the Participants.

These contracts are evergreen contracts and contain termination provisions, allowing the contract issuer to terminate with notice, at any time at fair value, and providing for automatic termination of the contract if the contract value or the fair value of the underlying portfolio equals zero. The issuer is obligated to pay the excess contract value when the fair value is below contract value at the time of termination. In addition, if the Company defaults in its obligations under the contract (including the issuer’s determination that the agreement constitutes a non-exempt prohibited transaction as defined under ERISA), and such default is not corrected within the time permitted by the contract, then the contract may be terminated by the issuer and the Plan will receive the fair value as of the date of termination.

Parties-in-interest are defined under Department of Labor regulations as any fiduciary of the Plan, any party rendering service to the Plan, the employer, and certain others.

At December 31, 2015, the Plan held 5,268,795 shares of Company common stock with a cost and fair value of $189,208,773 and $227,770,008, respectively. During 2015, the Plan purchased 879,500 shares at a cost of $36,272,199 and sold 921,100 shares valued at $38,778,584.

12

Ameren Corporation

Savings Investment Plan

Notes to Financial Statements

December 31, 2015 and 2014

At December 31, 2014, the Plan held 5,382,758 shares of Company common stock with a cost and fair value of $188,255,416 and $248,306,627, respectively. During 2014, the Plan purchased 676,200 shares at a cost of $27,122,220 and sold 863,800 shares valued at $35,008,574.

Dividend income from Company common stock was $10,865,043 and $8,501,427 for the years ended December 31, 2015 and December 31, 2014, respectively.

At December 31, 2015 and December 31, 2014, the Plan held shares in the Fidelity Management Trust Company Institutional Cash Portfolio. This portfolio is managed by the Trustee, and therefore, qualifies as party-in-interest transactions. Notes receivable from Participants also reflect party-in-interest transactions.

Fees paid by the Plan to the Trustee for recordkeeping and trust services were $1,060,655 and $1,094,988 for the years ended December 31, 2015 and December 31, 2014, respectively.

Fees paid to and investments issued by various Plan investment managers also reflect party-in-interest transactions.

These transactions are allowable party-in-interest transactions under Section 408(b)(8) of ERISA.

The following is a reconciliation of net assets available for benefits per the financial statements to the Form 5500 at December 31, 2015 and 2014:

Deemed distributions of notes receivable from Participants, resulting from defaults of notes receivable from Participants, are no longer considered assets of the Plan with respect to Form 5500 filings.

13

Ameren Corporation

Savings Investment Plan

Notes to Financial Statements

December 31, 2015 and 2014

The following is a reconciliation of net decrease in net assets available for benefits per the financial statements to net loss per the Form 5500 for the year ended December 31, 2015:

The Company obtained its latest determination letter September 18, 2013, in which the Internal Revenue Service stated that the Plan was in compliance with the applicable requirements of the Code. Although the Plan has been amended since receiving the determination letter, the Plan’s administrator believe that the Plan is designed and is currently being operated in compliance with the applicable requirements of the Code.

Accounting principles generally accepted in the United States of America require Plan management to evaluate tax positions taken by the Plan and recognize a tax liability (or asset) if the Plan has taken an uncertain position that more likely than not would not be sustained upon examination by the Internal Revenue Service. The Plan administrator has analyzed the tax positions taken by the Plan, and has concluded that as of December 31, 2015 and 2014, there are no uncertain positions taken or expected to be taken that would require recognition of a liability (or asset) or disclosure in the financial statements. The Plan is subject to routine audits by taxing jurisdictions; however, there are currently no audits for any tax periods in progress. The Plan administrator believes it is no longer subject to income tax examinations for years prior to 2012.

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Page 1 of 9

Ameren Corporation Savings Investment Plan

SCHEDULE H, Line 4i - SCHEDULE OF ASSETS (HELD AT END OF YEAR)

December 31, 2015

Name of plan sponsor: Ameren Corporation

Employer identification number: 43-1723446

Three-digit plan number: 003

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Page 2 of 9

Ameren Corporation Savings Investment Plan

SCHEDULE H, Line 4i - SCHEDULE OF ASSETS (HELD AT END OF YEAR)

December 31, 2015

Name of plan sponsor: Ameren Corporation

Employer identification number: 43-1723446

Three-digit plan number: 003

2

Page 3 of 9

Ameren Corporation Savings Investment Plan

SCHEDULE H, Line 4i - SCHEDULE OF ASSETS (HELD AT END OF YEAR)

December 31, 2015

Name of plan sponsor: Ameren Corporation

Employer identification number: 43-1723446

Three-digit plan number: 003

3

Page 4 of 9

Ameren Corporation Savings Investment Plan

SCHEDULE H, Line 4i - SCHEDULE OF ASSETS (HELD AT END OF YEAR)

December 31, 2015

Name of plan sponsor: Ameren Corporation

Employer identification number: 43-1723446

Three-digit plan number: 003

4

Page 5 of 9

Ameren Corporation Savings Investment Plan

SCHEDULE H, Line 4i - SCHEDULE OF ASSETS (HELD AT END OF YEAR)

December 31, 2015

Name of plan sponsor: Ameren Corporation

Employer identification number: 43-1723446

Three-digit plan number: 003

5

Page 6 of 9

Ameren Corporation Savings Investment Plan

SCHEDULE H, Line 4i - SCHEDULE OF ASSETS (HELD AT END OF YEAR)

December 31, 2015

Name of plan sponsor: Ameren Corporation

Employer identification number: 43-1723446

Three-digit plan number: 003