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Property and Plant, Net (Schedule of Capitalized Software, Future Amortization Expense) (Details) - Capitalized software costs
$ in Millions
Dec. 31, 2019
USD ($)
Finite-Lived Intangible Assets [Line Items]  
2020 $ 80
2021 74
2022 63
2023 50
2024 24
Union Electric Company  
Finite-Lived Intangible Assets [Line Items]  
2020 36
2021 34
2022 29
2023 24
2024 12
Ameren Illinois Company  
Finite-Lived Intangible Assets [Line Items]  
2020 41
2021 36
2022 32
2023 24
2024 $ 12