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Income Taxes | 9 Months Ended
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Sep. 30, 2025
Income Tax Disclosure [Abstract] |
Income Taxes | INCOME TAXES OBBBA The OBBBA was enacted in July 2025 and includes various income tax provisions, among other things. The OBBBA modified provisions of the IRA related to production and investment tax credits. The new law maintains production and investment tax credits for solar and wind projects that begin construction within one year of the OBBBA’s enactment and are placed in-service by the end of 2030. Projects that begin construction after one year from enactment of the OBBBA but are placed in service by the end of 2027 also remain eligible. The law provides investment tax credits for battery storage projects that begin construction by the end of 2033 and phase out by the end of 2035. Renewable energy projects that begin construction in 2026 and beyond that use a certain threshold percentage of materials from prohibited foreign entities, as defined in the OBBBA, are not eligible for the tax credits. Production tax credits associated with nuclear generation remain unchanged from the IRA and phase out by the end of 2032. Furthermore, the new law continues to allow for transferability of the production and investment tax credits to an unrelated party for cash but is restricted from being transferred to specified foreign entities, as defined in the OBBBA. Ameren is currently evaluating the OBBBA and guidance issued in connection with the OBBBA and does not expect any material impacts on its results of operations, financial position, and liquidity in 2025. Implementation of the OBBBA provisions is subject to additional guidance, regulations, interpretations, amendments, or technical corrections that may be issued by the IRS or United States Department of Treasury. The following table presents a reconciliation of the federal statutory corporate income tax rate to the effective income tax rate for the three and nine months ended September 30, 2025 and 2024:
| Ameren |  | Ameren Missouri |  | Ameren Illinois |
| 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |
Three Months |  |  |  |  |  |  |  |  |  |  |  |
Federal statutory corporate income tax rate | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |
Increases (decreases) from: |  |  |  |  |  |  |  |  |  |  |  |
Amortization of excess deferred taxes(a) | (7) |  |  | (9) |  |  | (9) |  |  | (15) |  |  | (4) |  |  | (4) |  |
Revaluation of excess deferred income taxes(b) | (7) |  |  | — |  |  | — |  |  | — |  |  | (14) |  |  | — |  |
Amortization of deferred investment tax credit | (1) |  |  | — |  |  | (1) |  |  | — |  |  | — |  |  | — |  |
Renewable and other tax credits(c) | (3) |  |  | (4) |  |  | (7) |  |  | (10) |  |  | — |  |  | — |  |
State tax | 5 |  |  | 4 |  |  | 3 |  |  | 3 |  |  | 7 |  |  | 7 |  |
Depreciation differences | (1) |  |  | — |  |  | (1) |  |  | (1) |  |  | (1) |  |  | — |  |
Other permanent items | — |  |  | (1) |  |  | — |  |  | — |  |  | 1 |  |  | — |  |
Effective income tax rate | 7 | % |  | 11 | % |  | 6 | % |  | (2) | % |  | 10 | % |  | 24 | % |
Nine Months |  |  |  |  |  |  |  |  |  |  |  |
Federal statutory corporate income tax rate | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |
Increases (decreases) from: |  |  |  |  |  |  |  |  |  |  |  |
Amortization of excess deferred taxes(a) | (7) |  |  | (8) |  |  | (9) |  |  | (14) |  |  | (4) |  |  | (4) |  |
Revaluation of excess deferred income taxes(b) | (3) |  |  | — |  |  | — |  |  | — |  |  | (4) |  |  | — |  |
Amortization of deferred investment tax credit | (1) |  |  | — |  |  | (1) |  |  | — |  |  | — |  |  | — |  |
Renewable and other tax credits(c) | (3) |  |  | (5) |  |  | (7) |  |  | (10) |  |  | — |  |  | — |  |
State tax | 5 |  |  | 5 |  |  | 3 |  |  | 3 |  |  | 7 |  |  | 7 |  |
Depreciation differences | (1) |  |  | — |  |  | (1) |  |  | (1) |  |  | — |  |  | — |  |
Effective income tax rate | 11 | % |  | 13 | % |  | 6 | % |  | (1) | % |  | 20 | % |  | 24 | % |
(a)Reflects the amortization of amounts resulting from the revaluation of deferred income taxes subject to regulatory ratemaking, which are being refunded to customers. Deferred income taxes are revalued when federal or state income tax rates change, and the offset to the revaluation of deferred income taxes subject to regulatory ratemaking is recorded to a regulatory asset or liability. (b)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. Accordingly, in the third quarter of 2025, Ameren and Ameren Illinois decreased income tax expense by $48 million and $23 million, respectively, to reflect the revaluation of excess deferred income tax regulatory liabilities resulting from TCJA for FERC-regulated jurisdictions pursuant to IRS guidance and recent FERC order. (c)The benefit of the renewable credits associated with Missouri renewable energy standard compliance is refunded to customers through the RESRAM. The benefit of the renewable credits associated with the production and investment tax credit tracker will be refunded to customers based on MoPSC approval in a regulatory rate review.

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