Rate And Regulatory Matters (Narrative-Federal) (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended
	Oct. 31, 2024	May 31, 2020	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Rate And Regulatory Matters [Line Items]
Capital expenditures				$ 1,064	$ 890
Forecast
Rate And Regulatory Matters [Line Items]
Capital expenditures			$ 1,300
Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Capital expenditures				363	$ 373
Current regulatory liabilities				89		$ 79
Midwest Independent Transmission System Operator, Inc | Final Rate Order
Rate And Regulatory Matters [Line Items]
Approved return on equity percentage	9.98%	10.02%
Current regulatory liabilities				11
Midwest Independent Transmission System Operator, Inc | Final Rate Order | Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Current regulatory liabilities				$ 7