Related Party Transactions (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Related Party Transaction [Line Items]
Interconnection agreement, optional termination period	3 years
Other assets	$ 1,123	$ 921
Ameren Illinois
Related Party Transaction [Line Items]
Other assets	697	603
Ameren Missouri
Related Party Transaction [Line Items]
Other assets	254	152
Ameren Illinois Capacity Supply Agreements with Ameren Missouri | Ameren Illinois | 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
Related Party Transaction [Line Items]
Other assets	$ 32	34
Ameren Services Support Services Agreement | Ameren Missouri
Related Party Transaction [Line Items]
Other assets	$ 29	$ 31