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Retirement Benefits (Summary Of Benefit Plan Costs Incurred) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | $ (84) | $ (148) | $ (4)
Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | (79) | (83) | (54)
Ameren Missouri | Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | (44) | (76) | (3)
Ameren Missouri | Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | (27) | (30) | (14)
Ameren Illinois | Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | (34) | (62) | 3
Ameren Illinois | Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | (52) | (54) | (41)
Other | Pension Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | (6) | (10) | (4)
Other | Postretirement Benefits |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Net periodic benefit cost | $ 0 | $ 1 | $ 1

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