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Retirement Benefits
 12 Months Ended
Dec. 31, 2025
Retirement Benefits [Abstract]  
RETIREMENT BENEFITS RETIREMENT BENEFITS
The primary objective of the Ameren pension and postretirement benefit plans is to provide eligible employees with pension and postretirement health care and life insurance benefits. Ameren has defined benefit pension plans covering substantially all of its employees and has a postretirement benefit plan covering non-union employees hired before October 2015 and union employees hired before January 2020. Ameren Missouri and Ameren Illinois each participate in Ameren’s single-employer pension and other postretirement plans. All non-union employees participate in a cash balance pension plan. Ameren Missouri union employees hired after June 2013, and Ameren Illinois union employees hired after mid-October 2012, participate in a cash balance pension plan. Ameren uses a measurement date of December 31 for its pension and postretirement benefit plans. Ameren’s qualified pension plan is the Ameren Retirement Plan. Ameren’s other postretirement plan is the Ameren Retiree Welfare Benefit Plan. Ameren also has an unfunded nonqualified pension plan, the Ameren Supplemental Retirement Plan, which is available to provide certain non-union employees and retirees with a supplemental benefit when their qualified pension plan benefits are capped in compliance with Internal Revenue Code limitations. Only Ameren subsidiaries participate in the plans listed above.
Ameren’s pension and other postretirement benefit plans were overfunded by $954 million and $734 million in the aggregate as of December 31, 2025 and 2024, respectively. These net assets are recorded in “Pension and other postretirement benefits,” “Other current liabilities,” and “Other deferred credits and liabilities” on Ameren’s consolidated balance sheet. The increase in the overfunded pension and postretirement benefit plans during 2025 was primarily the result of an increase in the actual return on plan assets of the pension and postretirement trusts and a 5-basis-point increase in the pension discount rate used to determine the present value of the obligation. The overfunded pension and other postretirement benefit plans also resulted in regulatory liabilities on Ameren’s, Ameren Missouri’s, and Ameren Illinois’ balance sheets.
The following table presents the net benefit liability/(asset) recorded on the balance sheets as of December 31, 2025 and 2024:
20252024
Ameren(a)
$(954)$(734)
Ameren Missouri(a)
(261)(201)
Ameren Illinois(a)
(563)(438)
(a)Liabilities associated with pension and other postretirement benefits are recorded in “Other current liabilities” and “Other deferred credits and liabilities” on Ameren’s, Ameren Missouri’s, and Ameren Illinois’ balance sheets.
In December 2025, Ameren, completed a contract transfer transaction with a third-party insurance company that transferred approximately $240 million of plan assets and plan obligations of the Ameren Retirement Plan, associated with approximately 4,200 former Ameren Missouri, Ameren Illinois, and Ameren Services employees, that will assume future and full responsibility to fund and administer their benefit payments. The transaction is designed to reduce potential volatility with the pension plan assets and liabilities and administrative costs. There was no change to the pension benefits for any participants because of the transfer. The transaction was funded by pension plan assets and resulted in an actuarial gain of $15 million, which will be amortized in net periodic benefit cost (income) over 10 years through the actuarial (gain) loss component beginning in 2026.
Ameren recognizes the overfunded and underfunded status of its pension and postretirement plans as an asset or a liability on its consolidated balance sheet, with offsetting entries to accumulated OCI and regulatory assets or liabilities. The following table presents the funded status of Ameren’s pension and postretirement benefit plans as of December 31, 2025 and 2024. It also provides the amounts included in regulatory assets or liabilities and accumulated OCI at December 31, 2025 and 2024, that have not been recognized in net periodic benefit costs.
20252024
Pension
Benefits		Postretirement
Benefits		Pension
Benefits		Postretirement
Benefits
Accumulated benefit obligation at end of year$3,773 $(a)$3,962 $(a)
Change in benefit obligation:
Net benefit obligation at beginning of year$4,134 $807 $4,258 $856 
Service cost82 10 88 12 
Interest cost234 45 222 44 
Participant contributions— 7 — 7 
Actuarial (gain) loss28 
(b)
5 (143)(51)
Contract transfer(c)
(240)— — — 
Benefits paid(299)(68)(291)(61)
Net benefit obligation at end of year3,939 806 4,134 807 
Change in plan assets:
Fair value of plan assets at beginning of year4,182 1,493 4,272 1,393 
Actual return on plan assets456 162 193 150 
Employer contributions3 3 8 4 
Participant contributions— 7 — 7 
Contract transfer(c)
(240)— — — 
Benefits paid(299)(68)(291)(61)
Fair value of plan assets at end of year4,102 1,597 4,182 1,493 
Funded status – surplus(163)(791)(48)(686)
Accrued benefit asset at December 31$(163)$(791)$(48)$(686)
Amounts recognized in the balance sheet consist of:
Noncurrent asset$(186)$(791)$(71)$(686)
Current liability(d)
2 — 2 — 
Noncurrent liability(e)
21 — 21 — 
Net asset recognized$(163)$(791)$(48)$(686)
Amounts recognized in regulatory assets or liabilities consist of:
Net actuarial (gain) loss$(45)$(404)$42 $(379)
Prior service credit— (18)— (21)
Amounts recognized in accumulated OCI (pretax) consist of:
Net actuarial (gain) loss22 (7)26 (7)
Total$(23)$(429)$68 $(407)
(a)Not applicable.
(b)Includes a $15 million gain from the contract transfer of defined benefit pension obligations and related plan assets to a third-party insurance company in December 2025 as described above.
(c)Represents the contract transfer of defined benefit pension obligations and related plan assets to a third-party insurance company in December 2025 as described above.
(d)Included in “Other current liabilities” on Ameren’s consolidated balance sheet.
(e)Included in “Other deferred credits and liabilities” on Ameren’s consolidated balance sheet.
The following table presents the assumptions used to determine our benefit obligations at December 31, 2025 and 2024:
Pension BenefitsPostretirement Benefits
2025202420252024
Discount rate at measurement date5.75 %5.70 %5.70 %5.70 %
Increase in future compensation4.00 4.00 4.00 4.00 
Cash balance pension plan interest crediting rate5.50 5.50 (a)(a)
Medical cost trend rate (initial)(b)
(a)(a)(c)(c)
Medical cost trend rate (ultimate)(b)
(a)(a)5.00 5.00 
(a)Not applicable.
(b)Initial and ultimate medical cost trend rate for certain Medicare-eligible participants was 2.50% at December 31, 2025 and 2024.
(c)Initial medical cost trend rates of 7.50% and 7.00% for both pre-Medicare plan participants and post-Medicare plan participants at December 31, 2025 and 2024, respectively, trend down to the ultimate rate by 2036 and 2033, respectively, with a 3.00% upward adjustment to the post-Medicare trend rate in 2024.
Ameren determines discount rate assumptions by identifying a theoretical settlement portfolio of high-quality corporate bonds sufficient to provide for a plan’s projected benefit payments. The settlement portfolio of bonds is selected from a pool of high-quality corporate bonds. A single discount rate is then determined; that rate results in a discounted value of the plan’s benefit payments that equates to the market value of the selected bonds. In 2025, Ameren elected to continue to use the Society of Actuaries mortality table and the Society of Actuaries 2020 Mortality Improvement Scale.
Funding
Pension benefits are based on the employees’ years of service, age, and compensation. Ameren’s pension plans are funded in compliance with income tax regulations, federal funding requirements, and other regulatory requirements. As a result, Ameren expects to fund its pension plans at a level equal to the greater of the pension cost or the legally required minimum contribution. Based on its assumptions at December 31, 2025, its investment performance in 2025, and its pension funding policy, Ameren expects to make annual contributions of approximately $45 million to $50 million in each of the next five years, with aggregate estimated contributions of $240 million. Ameren Missouri and Ameren Illinois estimate that their portion of the future funding requirements will be 35% and 45%, respectively. These estimated contributions may change based on actual investment performance, changes in interest rates, changes in our assumptions, changes in government regulations, and any voluntary contributions. Our funding policy for postretirement benefits is primarily to fund the Voluntary Employee Beneficiary Association (VEBA) trusts to match the annual postretirement expense.
The following table presents the cash contributions made to our defined benefit retirement plans and to our postretirement plan during 2025, 2024, and 2023:
Pension BenefitsPostretirement Benefits
202520242023202520242023
Ameren Missouri$1 $1 $1 $1 $2 $2 
Ameren Illinois1 1 2 1 1 1 
Ameren Services1 6 1 1 1 — 
Ameren$3 $8 $4 $3 $4 $3 
Investment Strategy and Policies
Ameren manages plan assets in accordance with the “prudent investor” guidelines contained in ERISA. The investment committee, which includes members of senior management, approves and implements investment strategy and asset allocation guidelines for the plan assets. The investment committee’s goals are twofold: first, to ensure that sufficient funds are available to provide the benefits at the time they are payable; and second, to maximize total return on plan assets and to minimize expense volatility consistent with its tolerance for risk. Ameren delegates the task of investment management to specialists in each asset class. As appropriate, Ameren provides each investment manager with guidelines that specify allowable and prohibited investment types. The investment committee regularly monitors manager performance and compliance with investment guidelines.
The expected return on plan assets assumption is based on historical and projected rates of return for current and planned asset classes in the investment portfolio. Projected rates of return for each asset class were estimated after an analysis of historical experience, future expectations, and the volatility of the various asset classes. After considering the target asset allocation for each asset class, we reviewed the overall expected rate of return for the portfolio for historical and expected experience of active portfolio management results compared with benchmark returns and for the effect of expenses paid from plan assets. Ameren will use an expected return on plan assets for its pension and postretirement plan assets of 6.75% in 2026.
Ameren’s investment committee strives to assemble a portfolio of diversified assets that does not create a significant concentration of risks. The investment committee develops asset allocation guidelines between asset classes, and it creates diversification through investments in assets that differ by type (equity, debt, real estate), duration, market capitalization, country, style (growth or value), and industry, among other factors. The diversification of assets is displayed in the target allocation table below. The investment committee also routinely rebalances the plan assets to adhere to the diversification goals. The investment committee’s strategy reduces the concentration of investment risk; however, Ameren is still subject to overall market risk.
Ameren’s investment committee developed and implemented a liability hedging investment strategy for its qualified pension plan designed to reduce interest rate risk as part of an objective for its long-term investment strategy. The plan invests in derivative instruments mainly consisting of interest rate futures intended to extend the duration of the pension plan assets so that the assets are more closely aligned with the duration of the liabilities. In addition, part of Ameren’s investment strategy includes participation in a securities lending program, which allows it to lend eligible securities to third party borrowers. All loans are collateralized by at least 103% of the loaned asset’s market value and the collateral is invested in the form of cash, government obligations, and U.S. agency obligations. Ameren’s fair value of securities loaned was $517 million and $454 million as of December 31, 2025 and 2024, respectively. Cash and securities obtained as collateral exceeded the fair value of the securities loaned as of December 31, 2025 and 2024.
The following table presents our target allocations and our pension and postretirement plans’ asset categories as of December 31, 2025 and 2024:
Asset
Category
Target Allocation
2025
Percentage of Plan Assets at December 31,
20252024
Pension Plan:
Cash and cash equivalents
0% – 5%
3 %3 %
Equity securities:
U.S. large-capitalization
10% – 20%
15 %16 %
U.S. small- and mid-capitalization
3% – 13%
9 %9 %
Global
10% – 20%
16 %15 %
International
4% – 14%
7 %9 %
Total equity
42% – 52%
47 %49 %
Debt securities
32% – 42%
34 %
(a)
35 %
(a)
Diversified credit
6% – 16%
10 %8 %
Real estate
0% – 10%
6 %5 %
Private equity
0% – 5%
— %(b)
Total 100 %100 %
Postretirement Plans:
Cash and cash equivalents
0% – 7%
2 %2 %
Equity securities:
U.S. large-capitalization
23% – 33%
33 %33 %
U.S. small- and mid-capitalization
3% – 13%
7 %8 %
Global
9% – 19%
13 %13 %
International
5% – 15%
8 %8 %
Total equity
55% – 65%
61 %62 %
Debt securities
33% – 43%
37 %36 %
Total 100 %100 %
(a)Includes interest rate futures derivative instruments.
(b)Less than 1% of plan assets.
In general, the United States large-capitalization equity investments are passively managed or indexed, whereas the international, global, United States small-capitalization, and United States mid-capitalization equity investments are actively managed by investment managers. Debt securities include a broad range of fixed-income vehicles. Debt security investments in high-yield securities and non-United-States-dollar-denominated securities are owned by the plans, but in limited quantities to reduce risk. Most of the debt security investments are under active management by investment managers. Diversified credit investments include but are not limited to, sub-investment grade rated bonds and loans, securitized credit, and emerging market debt. Real estate investments include private real estate vehicles; however, Ameren does not, by policy, hold direct investments in real estate property. In addition to the derivative investments included in the liability hedging investment strategy described above, Ameren’s investment committee also allows investment managers to use derivatives, such as index futures, foreign exchange futures, and options, in certain situations to increase or to reduce market exposure in an efficient and timely manner.
Fair Value Measurements of Plan Assets
Investments in the pension and postretirement benefit plans were stated at fair value as of December 31, 2025. Fair value is defined as the price that would be received for an asset in the principal or most advantageous market for the asset in an orderly transaction between market participants on the measurement date. Cash and cash equivalents have initial maturities of three months or less and are recorded at cost plus accrued interest. Investments traded in active markets on national or international securities exchanges are valued at closing prices on the measurement date or, if that is not a business day, on the last business day before that date. Securities traded in over-the-counter markets are valued by quoted market prices, broker or dealer quotations, or alternative pricing sources with reasonable levels of price transparency. Investments measured under NAV as a practical expedient are based on the fair values of the underlying assets provided by the funds and their administrators. The fair value of real estate investments is based on NAV; it is determined by annual appraisal reports prepared by an independent real estate appraiser. Investments measured at NAV often provide for daily, monthly, or quarterly redemptions with 60 or less days of notice depending on the fund. For some funds, redemption may also require approval from the fund’s board of directors. Derivative contracts are valued at fair value, as determined by the investment managers (or independent third parties on behalf of the investment managers), who use proprietary models and take into consideration exchange quotations on underlying instruments, dealer quotations, and other market information.
The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the pension plans’ assets measured at fair value and NAV as of December 31, 2025 and 2024:
December 31, 2025December 31, 2024
Level 1Level 2NAVTotalLevel 1Level 2NAVTotal
Cash and cash equivalents$— $— $96 $96 $— $— $75 $75 
Equity securities:
U.S. large-capitalization— — 648 648 — — 689 689 
U.S. small- and mid-capitalization382 — — 382 375 — — 375 
International120 — 203 323 182 — 226 408 
Global— — 671 671 — — 680 680 
Debt securities:
Corporate bonds— 418 — 418 — 463 — 463 
Municipal bonds— 36 — 36 — 36 — 36 
U.S. Treasury and agency securities— 1,016 — 1,016 — 1,032 — 1,032 
Diversified credit— — 456 456 — — 344 344 
Other(10)7 — (3)(17)11 — (6)
Real estate— — 243 243 — — 233 233 
Total$492 $1,477 $2,317 $4,286 $540 $1,542 $2,247 $4,329 
Less: Medical benefit assets(a)
(222)(200)
Plus: Net receivables (payables)(b)
38 53 
Fair value of pension plans’ assets$4,102 $4,182 
(a)Medical benefit (health and welfare) component for accounts maintained in accordance with Section 401(h) of the Internal Revenue Code to fund a portion of the postretirement obligation.
(b)Net of receivables related to pending securities sales and payables related to pending securities purchases.
The following table sets forth, by level within the fair value hierarchy discussed in Note 8 – Fair Value Measurements, the postretirement benefit plans’ assets measured at fair value and NAV as of December 31, 2025 and 2024:
December 31, 2025December 31, 2024
Level 1Level 2NAVTotalLevel 1Level 2NAVTotal
Cash and cash equivalents$18 $— $— $18 $25 $— $— $25 
Equity securities:
U.S. large-capitalization353 — 106 459 332 — 91 423 
U.S. small- and mid-capitalization100 — — 100 106 — — 106 
International56 — 59 115 54 — 52 106 
Global— — 178 178 — — 165 165 
Debt securities:
Municipal bonds— 187 — 187 — 173 — 173 
Other— — 315 315 — — 293 293 
Total$527 $187 $658 $1,372 $517 $173 $601 $1,291 
Plus: Medical benefit assets(a)
222 200 
Plus: Net receivables(b)
  3 2 
Fair value of postretirement benefit plans’ assets  $1,597 $1,493 
(a)Medical benefit (health and welfare) component for accounts maintained in accordance with Section 401(h) of the Internal Revenue Code to fund a portion of the postretirement obligation. These 401(h) assets are included in the pension plan assets shown above.
(b)Net of receivables related to pending securities sales and payables related to pending securities purchases.
Net Periodic Benefit Cost
The following table presents the components of the net periodic benefit cost (income) of Ameren’s pension and postretirement benefit plans during 2025, 2024, and 2023:
Pension BenefitsPostretirement Benefits
202520242023202520242023
Service cost(a)
$82 $88 $79 $10 $12 $12 
Non-service cost components:
Interest cost234 222 221 45 44 45 
Expected return on plan assets(b)
(303)(327)(333)(94)(93)(91)
Amortization of(b):
Prior service cost (credit)— — — (4)(4)(4)
Actuarial (gain)(34)(67)(115)(38)(38)(45)
Total non-service cost components(c)
$(103)$(172)$(227)$(91)$(91)$(95)
Net periodic benefit cost (income)(d)
$(21)$(84)$(148)$(81)$(79)$(83)
(a)Service cost, net of capitalization, is reflected in “Operating Expenses - Other operations and maintenance” on Ameren’s statement of income.
(b)Prior service cost (credit) is amortized on a straight-line basis over the average future service of active participants benefiting under the plan amendment. Net actuarial gains or losses subject to amortization are amortized on a straight-line basis over 10 years. Expected return on plan assets is based on a market-related value of assets that recognizes asset (gains) losses over 4 years.
(c)Non-service cost components are reflected in “Other Income, Net” on Ameren’s consolidated statement of income. See Note 6 – Other Income, Net for additional information.
(d)Does not include the impact of the tracker for the difference between the level of pension and postretirement benefit costs (income) incurred by Ameren Missouri under GAAP and the level of such costs included in rates.
The Ameren Companies are responsible for their share of the pension and postretirement benefit costs (income). The following table presents the pension and postretirement benefit costs (income) incurred for the years ended December 31, 2025, 2024, and 2023:
Pension CostsPostretirement Costs
202520242023202520242023
Ameren Missouri(a)
$(14)$(44)$(76)$(28)$(27)$(30)
Ameren Illinois(4)(34)(62)(53)(52)(54)
Other(3)(6)(10)— — 1 
Ameren$(21)$(84)$(148)$(81)$(79)$(83)
(a)Does not include the impact of the tracker for the difference between the level of pension and postretirement benefit costs (income) incurred by Ameren Missouri under GAAP and the level of such costs included in customer rates.
The expected pension and postretirement benefit payments from qualified trust and company funds, which reflect expected future service, as of December 31, 2025, are as follows:
Pension BenefitsPostretirement Benefits
Paid from
Qualified
Trust Funds		Paid from
Company
Funds		Paid from
Qualified
Trust Funds		Paid from
Company
Funds
2026$262 $2 $59 $3 
2027267 2 59 3 
2028271 2 59 3 
2029275 2 58 3 
2030279 2 58 3 
2031 – 20351,424 14 288 13 
The following table presents the assumptions used to determine net periodic benefit cost for our pension and postretirement benefit plans for the years ended December 31, 2025, 2024, and 2023:
Pension BenefitsPostretirement Benefits
202520242023202520242023
Discount rate at measurement date5.70 %5.25 %5.55 %5.70 %5.25 %5.55 %
Expected return on plan assets6.75 6.75 6.75 6.75 6.75 6.75 
Increase in future compensation(a)
4.00 3.50 3.50 4.00 3.50 3.50 
Cash balance pension plan interest crediting rate(b)
5.50 5.50 5.00 (c)(c)(c)
Medical cost trend rate (initial)(d)
(c)(c)(c)(e)(f)(g)
Medical cost trend rate (ultimate)(d)
(c)(c)(c)5.00 5.00 5.00 
(a)Increase in future compensation is 4.00% for the year ended December 31, 2025, 4.00% for 2024 and 3.50% thereafter for the year ended December 31, 2024, and 4.50% for 2023, 4.00% for 2024, and 3.50% thereafter for the year ended December 31, 2023.
(b)Cash balance pension plan interest crediting rate is 5.20% for 2025 and 5.50% thereafter for the year ended December 31, 2025, was 6.42% for 2024, and 5.50% thereafter for the year ended December 31, 2024, and 5.50% for 2023 and 2024, and 5.00% thereafter for the year ended December 31, 2023.
(c)Not applicable.
(d)Initial and ultimate medical cost trend rate for certain Medicare-eligible participants is 2.50% for the years ended December 31, 2025, 2024, and 2023.
(e)Initial medical cost trend rates of 7.00% for pre-Medicare plan participants and 7.00% for post-Medicare plan participants trend down to the ultimate rate by 2033 with a 3.00% upward adjustment to the post-Medicare trend rate in 2025.
(f)Initial medical cost trend rates of 6.93% for pre-Medicare plan participants and 6.50% for post-Medicare plan participants trend down to the ultimate rate by 2030, with a 3.00% upward adjustment to the post-Medicare trend rate in 2025.
(g)Initial medical cost trend rates of 7.25% for pre-Medicare plan participants and 6.75% for post-Medicare plan participants trend down to the ultimate rate by 2030, with a 3.00% upward adjustment to the post-Medicare trend rate in 2025.
Other
Ameren sponsors a 401(k) plan for eligible employees. The Ameren 401(k) plan covered all eligible Ameren employees at December 31, 2025. The plan allows employees to contribute a portion of their compensation in accordance with specific guidelines. Ameren matches a percentage of the employee contributions up to certain limits. The following table presents the portion of the matching contribution to the Ameren 401(k) plan attributable to each of the Ameren Companies for the years ended December 31, 2025, 2024, and 2023:
202520242023
Ameren Missouri$26 $26 $27 
Ameren Illinois22 22 21 
Other1 1 1 
Ameren$49 $49 $49