Rate and Regulatory Matters (Narrative-Federal) (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended
	Oct. 31, 2024	May 31, 2020	Dec. 31, 2024	Dec. 31, 2023
Ameren Illinois
Public Utilities, General Disclosures [Line Items]
Current regulatory liabilities			$ 79	$ 71
Final Rate Order | Midwest Independent Transmission System Operator, Inc
Public Utilities, General Disclosures [Line Items]
Public Utilities, Approved Return on Equity, Percentage	9.98%	10.02%
Expense recognized due to lower FERC-allowed base ROE			2
Current regulatory liabilities			12
Final Rate Order | Midwest Independent Transmission System Operator, Inc | Electric
Public Utilities, General Disclosures [Line Items]
Revenue reduction due to lower FERC-allowed base ROE			10
Final Rate Order | Midwest Independent Transmission System Operator, Inc | Ameren Illinois
Public Utilities, General Disclosures [Line Items]
Expense recognized due to lower FERC-allowed base ROE			1
Current regulatory liabilities			8
Final Rate Order | Midwest Independent Transmission System Operator, Inc | Ameren Illinois | Electric
Public Utilities, General Disclosures [Line Items]
Revenue reduction due to lower FERC-allowed base ROE			$ 7