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Retirement Benefits (Summary Of Benefit Plan Costs Incurred) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | $ (4) | $ 62 | $ 52
Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | (54) | (34) | (35)
Union Electric Company | Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | (3) | 29 | 22
Union Electric Company | Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | (14) | (4) | (5)
Ameren Illinois Company | Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | 3 | 34 | 32
Ameren Illinois Company | Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | (41) | (31) | (31)
Other | Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | (4) | (1) | (2)
Other | Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | $ 1 | $ 1 | $ 1

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