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v3.25.4

Retirement Benefits (Narrative) (Details) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2026 | Dec. 31, 2025 USD ($) yr employee | Dec. 31, 2024 USD ($) | Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Funded (Unfunded) Status of Plan |  | $ 954 | $ 734 |
Defined Benefit Plan Assumptions Used Calculating Benefit Obligation, Change in Discount Rate |  | 0.05% |  |
Defined benefit plan estimated future employer contributions over next five years |  | $ 240 |  |
Collateralized loan percentage compared to asset's market value |  | 103.00% |  |
Securities Loaned |  | $ 517 | 454 |
Minimum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined benefit plan estimated future employer contributions over next five years |  | 45 |  |
Maximum |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined benefit plan estimated future employer contributions over next five years |  | 50 |  |
Pension Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Funded (Unfunded) Status of Plan |  | $ 163 | $ 48 |
Expected return on plan assets |  | 6.75% | 6.75% | 6.75%
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Assets Transferred to (from) Plan |  | $ 240 | $ 0 |
Plan amendments |  | $ 240 | $ 0 |
Defined Benefit Plan Number Of Covered Employees By Plan | employee |  | 4,200 |  |
Defined Benefit Plan Plan Assets Pre Tax Gain |  | $ 15 |  |
Defined Benefit Plan Plan Assets Pre Tax Gain Amortization Period | yr |  | 10 |  |
Pension Benefits | Forecast |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Expected return on plan assets | 6.75% |  |  |
Ameren Missouri | Pension Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Future funding requirement, percentage |  | 35.00% |  |
Ameren Illinois | Pension Benefits |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Future funding requirement, percentage |  | 45.00% |  |

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- Definition The employer's best estimate, as soon as it can be reasonably determined, of the contributions expected to be paid to the plan during the next five fiscal years beginning after the date of the latest statement of financial position. Estimated contributions may be presented in the aggregate combining (1) contributions required by funding regulations or laws, (2) discretionary contributions, and (3) noncash contributions. + References No definition available. + Details
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- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (j)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-5 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 8 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-8 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (k)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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