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Property and Plant, Net (Schedule of Capitalized Software, Future Amortization Expense) (Details) - Capitalized software costs
$ in Millions
Dec. 31, 2021
USD ($)
Finite-Lived Intangible Assets [Line Items]  
2022 $ 135
2023 119
2024 87
2025 47
2026 21
Union Electric Company  
Finite-Lived Intangible Assets [Line Items]  
2022 75
2023 69
2024 54
2025 31
2026 14
Ameren Illinois Company  
Finite-Lived Intangible Assets [Line Items]  
2022 56
2023 47
2024 31
2025 14
2026 $ 6