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Income Taxes (Tables) | 12 Months Ended
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Dec. 31, 2025
Income Tax Disclosure [Abstract] |
Schedule Of Effective Income Tax Rate Reconciliation | The following table presents the principal reasons for the difference between the effective income tax expense and rate and the federal statutory corporate income tax expense and rate for the years ended December 31, 2025, 2024, and 2023:
| 2025 | 2024 | 2023
| Amount |  | Effective Tax Rate | Amount |  | Effective Tax Rate | Amount |  | Effective Tax Rate
Ameren |  |  |  |  |  |  |  |  |
Federal statutory corporate income tax expense and rate | $ | 335 |  |  | 21 | % | $ | 267 |  |  | 21 | % | $ | 282 |  |  | 21 | %
State and local taxes, net of federal income tax(a) | 74 |  |  | 5 |  | 61 |  |  | 5 |  | 64 |  |  | 5 |
Tax credits |  |  |  |  |  |  |  |  |
Renewable energy tax credits(b) | (61) |  |  | (4) |  | (117) |  |  | (9) |  | (52) |  |  | (4) |
Other | (3) |  |  | — |  | (7) |  |  | — |  | (6) |  |  | — |
Changes in valuation allowances | — |  |  | — |  | (4) |  |  | — |  | 5 |  |  | — |
Nontaxable or nondeductible items | (2) |  |  | — |  | 1 |  |  | — |  | (5) |  |  | — |
Other adjustments |  |  |  |  |  |  |  |  |
Amortization of excess deferred income taxes(c) | (107) |  |  | (7) |  | (112) |  |  | (9) |  | (98) |  |  | (8) |
Revaluation of excess deferred income taxes(d) | (86) |  |  | (5) |  | — |  |  | — |  | — |  |  | — |
Depreciation differences | (14) |  |  | (1) |  | (8) |  |  | (1) |  | (7) |  |  | — |
Other | — |  |  | — |  | 2 |  |  | — |  | — |  |  | — |
Effective income tax expense and rate | $ | 136 |  |  | 9 | % | $ | 83 |  |  | 7 | % | $ | 183 |  |  | 14 | %
Ameren Missouri |  |  |  |  |  |  |  |  |
Federal statutory corporate income tax expense and rate | $ | 166 |  |  | 21 | % | $ | 100 |  |  | 21 | % | $ | 113 |  |  | 21 | %
State and local taxes, net of federal income tax(a) | 21 |  |  | 3 |  | 13 |  |  | 3 |  | 14 |  |  | 3 |
Tax credits |  |  |  |  |  |  |  |  |
Renewable energy tax credits(b) | (61) |  |  | (8) |  | (113) |  |  | (24) |  | (49) |  |  | (10) |
Other | (3) |  |  | — |  | (4) |  |  | (1) |  | (5) |  |  | (1) |
Nontaxable or nondeductible items | 1 |  |  | — |  | 1 |  |  | — |  | (1) |  |  | — |
Other adjustments |  |  |  |  |  |  |  |  |
Amortization of excess deferred income taxes(c) | (75) |  |  | (10) |  | (79) |  |  | (17) |  | (80) |  |  | (15) |
Depreciation differences | (6) |  |  | (1) |  | (5) |  |  | — |  | — |  |  | — |
Effective income tax expense (benefit) and rate | $ | 43 |  |  | 5 | % | (87) |  |  | (18) | % | $ | (8) |  |  | (2) | %
Ameren Illinois |  |  |  |  |  |  |  |  |
Federal statutory corporate income tax expense and rate | $ | 187 |  |  | 21 | % | $ | 171 |  |  | 21 | % | $ | 172 |  |  | 21 | %
State and local taxes, net of federal income tax(a) | 66 |  |  | 7 |  | 62 |  |  | 7 |  | 61 |  |  | 7 |
Tax credits |  |  |  |  |  |  |  |  |
Renewable energy tax credits | — |  |  | — |  | (3) |  |  | — |  | — |  |  | — |
Other | (1) |  |  | — |  | (2) |  |  | — |  | (1) |  |  | — |
Nontaxable or nondeductible items | (1) |  |  | — |  | — |  |  | — |  | (1) |  |  | — |
Other adjustments |  |  |  |  |  |  |  |  |
Amortization of excess deferred income taxes(c) | (31) |  |  | (3) |  | (32) |  |  | (4) |  | (17) |  |  | (2) |
Revaluation of excess deferred income taxes(d) | (61) |  |  | (7) |  | — |  |  | — |  | — |  |  | — |
Depreciation differences | (9) |  |  | (1) |  | (3) |  |  | — |  | (5) |  |  | — |
Other | 3 |  |  | — |  | — |  |  | — |  | — |  |  | — |
Effective income tax expense and rate | $ | 153 |  |  | 17 | % | $ | 193 |  |  | 24 | % | $ | 209 |  |  | 26 | %
(a)State taxes in Missouri and Illinois made up the majority of the tax effect in this category for Ameren, Ameren Missouri, and Ameren Illinois. (b)The benefit of the credits associated with Missouri renewable energy standard compliance is refunded to customers through the RESRAM. The benefit of the credits associated with the production and investment tax credit tracker will be refunded to customers based on MoPSC approval in a regulatory rate review. (c)Reflects the amortization of a regulatory liability resulting from the revaluation of accumulated deferred income taxes subject to regulatory ratemaking, which are being refunded to customers. (d)In 2024, the IRS issued a series of private letter rulings to another taxpayer, which provided guidance on applying IRS normalization rules to the calculation of tax benefits applicable to the ratemaking treatment related to net operating loss carryforwards. The rulings concluded that, for ratemaking purposes, net operating loss carryforwards should be reflected on a separate company basis and should not be reduced by payments received for the utilization of losses by other affiliates under a tax allocation agreement. In 2025, the FERC issued an order reflecting implementation of the rules for the other taxpayer who had a similar fact pattern as Ameren Illinois and ATXI. In addition, in 2025, the ICC issued orders in Ameren Illinois’ 2024 electric distribution service revenue requirement reconciliation adjustment proceeding and in its January 2025 natural gas rate review addressing the impacts of the private letter rulings. Accordingly, in 2025, Ameren and Ameren Illinois decreased income tax expense by $86 million and $61 million, respectively, to reflect the revaluation of excess deferred income tax regulatory liabilities resulting from TCJA for FERC-regulated and ICC-regulated jurisdictions pursuant to IRS guidance and recent FERC and ICC orders.
Schedule Of Components Of Income Tax Expense (Benefit) | The following table presents the components of income tax expense (benefit) for the years ended December 31, 2025, 2024, and 2023:
| Ameren Missouri |  | Ameren Illinois |  | Other |  | Ameren
2025 |  |  |  |  |  |  |
Current taxes: |  |  |  |  |  |  |
Federal | $ | (140) |  |  | $ | 64 |  |  | $ | (41) |  |  | $ | (117) |
State | (2) |  |  | 19 |  |  | (17) |  |  | — |
Deferred taxes: |  |  |  |  |  |  |
Federal | 233 |  |  | 38 |  |  | (2) |  |  | 269 |
State | 38 |  |  | 63 |  |  | 1 |  |  | 102 |
Amortization of excess deferred income taxes | (75) |  |  | (31) |  |  | (1) |  |  | (107) |
Amortization of deferred investment tax credits | (11) |  |  | — |  |  | — |  |  | (11) |
Total income tax expense (benefit) | $ | 43 |  |  | $ | 153 |  |  | $ | (60) |  |  | $ | 136 |
2024 |  |  |  |  |  |  |
Current taxes: |  |  |  |  |  |  |
Federal | $ | (55) |  |  | $ | 5 |  |  | $ | 7 |  |  | $ | (43) |
State | (3) |  |  | — |  |  | 2 |  |  | (1) |
Deferred taxes: |  |  |  |  |  |  |
Federal | 45 |  |  | 144 |  |  | (12) |  |  | 177 |
State | 8 |  |  | 76 |  |  | (19) |  |  | 65 |
Amortization of excess deferred income taxes | (79) |  |  | (32) |  |  | (1) |  |  | (112) |
Amortization of deferred investment tax credits | (3) |  |  | — |  |  | — |  |  | (3) |
Total income tax expense (benefit) | $ | (87) |  |  | $ | 193 |  |  | $ | (23) |  |  | $ | 83 |
2023 |  |  |  |  |  |  |
Current taxes: |  |  |  |  |  |  |
Federal | $ | (37) |  |  | $ | 27 |  |  | $ | (37) |  |  | $ | (47) |
State | 1 |  |  | 5 |  |  | (5) |  |  | 1 |
Deferred taxes: |  |  |  |  |  |  |
Federal | 102 |  |  | 123 |  |  | 35 |  |  | 260 |
State | 9 |  |  | 71 |  |  | (10) |  |  | 70 |
Amortization of excess deferred income taxes | (80) |  |  | (17) |  |  | (1) |  |  | (98) |
Amortization of deferred investment tax credits | (3) |  |  | — |  |  | — |  |  | (3) |
Total income tax expense (benefit) | $ | (8) |  |  | $ | 209 |  |  | $ | (18) |  |  | $ | 183 |
Schedule Of Deferred Tax Assets And Liabilities Resulting From Temporary Differences | The following table presents the accumulated deferred income tax assets and liabilities recorded as a result of temporary differences and accumulated deferred production and investment tax credits at December 31, 2025 and 2024:
| Ameren Missouri |  | Ameren Illinois |  | Other |  | Ameren
2025 |  |  |  |  |  |  |
Accumulated deferred income taxes, net liability (asset): |  |  |  |  |  |  |
Plant-related | $ | 2,652 |  |  | $ | 2,416 |  |  | $ | 244 |  |  | $ | 5,312 |
Regulatory assets and liabilities, net | (179) |  |  | (130) |  |  | (16) |  |  | (325) |
Deferred employee benefit costs | (2) |  |  | 89 |  |  | (16) |  |  | 71 |
Tax carryforwards | (190) |  |  | (45) |  |  | (108) |  |  | (343) |
Other | 161 |  |  | 21 |  |  | 21 |  |  | 203 |
Total net accumulated deferred income tax liabilities (assets) | 2,442 |  |  | 2,351 |  |  | 125 |  |  | 4,918 |
Accumulated deferred investment tax credits | 260 |  |  | 3 |  |  | — |  |  | 263 |
Accumulated deferred income taxes and investment tax credits | $ | 2,702 |  |  | $ | 2,354 |  |  | $ | 125 |  |  | $ | 5,181 |
2024 |  |  |  |  |  |  |
Accumulated deferred income taxes, net liability (asset): |  |  |  |  |  |  |
Plant-related | $ | 2,429 |  |  | $ | 2,250 |  |  | $ | 261 |  |  | $ | 4,940 |
Regulatory assets and liabilities, net | (193) |  |  | (170) |  |  | (22) |  |  | (385) |
Deferred employee benefit costs | (25) |  |  | 77 |  |  | (25) |  |  | 27 |
Tax carryforwards | (355) |  |  | (45) |  |  | (103) |  |  | (503) |
Other | 131 |  |  | 28 |  |  | 3 |  |  | 162 |
Total net accumulated deferred income tax liabilities (assets) | 1,987 |  |  | 2,140 |  |  | 114 |  |  | 4,241 |
Accumulated deferred investment tax credits | 230 |  |  | 3 |  |  | — |  |  | 233 |
Accumulated deferred income taxes and investment tax credits | $ | 2,217 |  |  | $ | 2,143 |  |  | $ | 114 |  |  | $ | 4,474 |
Schedule Of Net Operating Loss Carryforwards And Tax Credit Carryforwards | The following table presents the components of accumulated deferred income tax assets relating to net operating loss carryforwards and tax credit carryforwards at December 31, 2025 and 2024:
| Ameren Missouri |  | Ameren Illinois |  | Other |  | Ameren
2025 |  |  |  |  |  |  |
Net operating loss carryforwards: |  |  |  |  |  |  |
Federal(a) | $ | 53 |  |  | $ | — |  |  | $ | 24 |  |  | $ | 77 |
State(b) | 9 |  |  | 34 |  |  | 45 |  |  | 88 |
Total net operating loss carryforwards | $ | 62 |  |  | $ | 34 |  |  | $ | 69 |  |  | $ | 165 |
Tax credit carryforwards: |  |  |  |  |  |  |
Federal(c) | $ | 128 |  |  | $ | 9 |  |  | $ | 39 |  |  | $ | 176 |
State(d) | — |  |  | 2 |  |  | — |  |  | 2 |
Total tax credit carryforwards | $ | 128 |  |  | $ | 11 |  |  | $ | 39 |  |  | $ | 178 |
2024 |  |  |  |  |  |  |
Net operating loss carryforwards: |  |  |  |  |  |  |
Federal | $ | — |  |  | $ | — |  |  | $ | 30 |  |  | $ | 30 |
State | — |  |  | 34 |  |  | 29 |  |  | 63 |
Total net operating loss carryforwards | $ | — |  |  | $ | 34 |  |  | $ | 59 |  |  | $ | 93 |
Tax credit carryforwards: |  |  |  |  |  |  |
Federal | $ | 355 |  |  | $ | 9 |  |  | $ | 44 |  |  | $ | 408 |
State | — |  |  | 2 |  |  | — |  |  | 2 |
Total tax credit carryforwards | $ | 355 |  |  | $ | 11 |  |  | $ | 44 |  |  | $ | 410 |
(a)No expiration date. (b)Will expire between 2039 and 2047. (c)Will expire between 2032 and 2045. (d)Will expire between 2026 and 2030.
Schedule of Cash Flow, Supplemental Disclosures | The following table presents the total income taxes paid, net of refunds, including production and investment tax credit sale proceeds, for the years ended December 31, 2025, 2024, and 2023:
| Ameren Missouri(a) |  | Ameren Illinois(a) |  | Ameren
2025 |  | 2024 |  |  | 2023 |  | 2025 |  | 2024 |  | 2023 |  | 2025 |  | 2024 |  | 2023
Federal(b) | $ | (350) |  |  | $ | (131) |  |  |  | $ | (24) |  |  | $ | 79 |  |  | $ | (25) |  |  | $ | 76 |  |  | $ | (309) |  |  | $ | (92) |  |  | $ | (37) |
State |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Illinois | — |  |  | — |  |  |  | — |  |  | 39 |  |  | (21) |  |  | 26 |  |  | 34 |  |  | (12) |  |  | 28 |
Missouri | (9) |  |  | (5) |  |  |  | 5 |  |  | — |  |  | — |  |  | — |  |  | (37) |  |  | 12 |  |  | (15) |
Total taxes paid | $ | (359) |  |  | $ | (136) |  |  |  | $ | (19) |  |  | $ | 118 |  |  | $ | (46) |  |  | $ | 102 |  |  | $ | (312) |  |  | $ | (92) |  |  | $ | (24) |
(a)Amounts represent income tax paid, net of refunds, to Ameren (parent), pursuant to the tax allocation agreement. See Note 1 – Summary of Significant Accounting Policies – Income Taxes for additional information. (b)Includes production and investment tax credit sale proceeds for Ameren and Ameren Missouri of $314 million, $95 million, and $49 million for the years ended December 31, 2025, 2024, and 2023, respectively. The following table provides noncash financing and investing activity excluded from the statements of cash flows for the years ended December 31, 2025, 2024, and 2023:
| December 31, 2025 |  | December 31, 2024 |  | December 31, 2023
Ameren | Ameren Missouri |  | Ameren Illinois |  | Ameren | Ameren Missouri | Ameren Illinois |  | Ameren | Ameren Missouri | Ameren Illinois
Investing |  |  |  |  |  |  |  |  |  |  |  |
Accrued capital expenditures, including nuclear fuel expenditures | $ | 622 |  | $ | 355 |  |  | $ | 210 |  |  | $ | 480 |  | $ | 303 |  | $ | 157 |  |  | $ | 518 |  | $ | 270 |  | $ | 212 |
Net realized and unrealized gain (loss) – nuclear decommissioning trust fund | 160 |  | 160 |  |  | — |  |  | 165 |  | 165 |  | — |  |  | 167 |  | 167 |  | — |
Return of investment in industrial development revenue bonds(a) | — |  | — |  |  | — |  |  | — |  | — |  | — |  |  | 240 |  | 240 |  | — |
Financing |  |  |  |  |  |  |  |  |  |  |  |
Issuance of common stock for stock-based compensation | $ | 25 |  | $ | — |  |  | $ | — |  |  | $ | 16 |  | $ | — |  | $ | — |  |  | $ | 40 |  | $ | — |  | $ | — |
Issuance of common stock under the DRPlus | 7 |  | — |  |  | — |  |  | 7 |  | — |  | — |  |  | 7 |  | — |  | — |
Termination of a financing agreement(a) | — |  | — |  |  | — |  |  | — |  | — |  | — |  |  | 240 |  | 240 |  | — |
(a)In January 2023, Ameren Missouri and Audrain County mutually agreed to terminate a financing obligation agreement related to the CT energy center in Audrain County, which was scheduled to expire in December 2023. No cash was exchanged in connection with the termination of the agreement as the $240 million principal amount of the financing obligation due from Ameren Missouri was equal to the amount of bond service payments due to Ameren Missouri.

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