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v3.25.1

Retirement Benefits (Summary of Benefit Plan Costs Incurred) (Details) - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2025 | Mar. 31, 2024
Pension Plan |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Net periodic benefit cost | $ (7) | $ (23)
Pension Plan | Union Electric Company |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Net periodic benefit cost | (4) | (12)
Pension Plan | Ameren Illinois Company |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Net periodic benefit cost | (2) | (9)
Pension Plan | Other Affiliated Entities And Intercompany Eliminations |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Net periodic benefit cost | (1) | (2)
Other Postretirement Benefit Plan, Defined Benefit |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Net periodic benefit cost | (20) | (20)
Other Postretirement Benefit Plan, Defined Benefit | Union Electric Company |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Net periodic benefit cost | (7) | (7)
Other Postretirement Benefit Plan, Defined Benefit | Ameren Illinois Company |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Net periodic benefit cost | (13) | (13)
Other Postretirement Benefit Plan, Defined Benefit | Other Affiliated Entities And Intercompany Eliminations |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] |  |
Net periodic benefit cost | $ 0 | $ 0

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