Rate And Regulatory Matters (Narrative-Federal) (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended
	Oct. 31, 2024	May 31, 2020	Sep. 30, 2024	Dec. 31, 2023
Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Current regulatory liabilities			$ 50	$ 71
Midwest Independent Transmission System Operator, Inc | Final Rate Order
Rate And Regulatory Matters [Line Items]
Approved return on equity percentage		10.02%
Expense recognized due to lower FERC-allowed base ROE			2
Current regulatory liabilities			12
Midwest Independent Transmission System Operator, Inc | Final Rate Order | Electric
Rate And Regulatory Matters [Line Items]
Revenue reduction due to lower FERC-allowed base ROE			10
Midwest Independent Transmission System Operator, Inc | Final Rate Order | Subsequent Event
Rate And Regulatory Matters [Line Items]
Approved return on equity percentage	9.98%
Midwest Independent Transmission System Operator, Inc | Final Rate Order | Ameren Illinois Company
Rate And Regulatory Matters [Line Items]
Expense recognized due to lower FERC-allowed base ROE			1
Current regulatory liabilities			8
Midwest Independent Transmission System Operator, Inc | Final Rate Order | Ameren Illinois Company | Electric
Rate And Regulatory Matters [Line Items]
Revenue reduction due to lower FERC-allowed base ROE			$ 7