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Related Party Transactions (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2022 | Dec. 31, 2021
Related Party Transaction [Line Items] |  |
Interconnection agreement, optional termination period | 3 years |
Ameren Illinois Capacity Supply Agreements with Ameren Missouri | Ameren Illinois Company | 2021 Procurements |  |
Related Party Transaction [Line Items] |  |
Energy Supply Agreements Amount | $ 2 |
Ameren Services Support Services Agreement |  |
Related Party Transaction [Line Items] |  |
Support services agreement, optional termination period | 60 days |
Ameren Services Support Services Agreement | Ameren Illinois Company |  |
Related Party Transaction [Line Items] |  |
Due from Related Parties | $ 43 | $ 80
Ameren Services Support Services Agreement | Union Electric Company |  |
Related Party Transaction [Line Items] |  |
Due from Related Parties | $ 41 | $ 77

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