Supplemental Information (Supplemental Cash Flow Information) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures, including nuclear fuel expenditures	$ 404	$ 518
Net realized and unrealized gain – nuclear decommissioning trust fund	163	66
Return on investment in industrial development revenue bonds	0	240
Termination of a financing obligation	0	240
Issuance of common stock for stock-based compensation
Supplemental Cash Flow Information [Line Items]
Stock Issued	16	37
Issuance of common stock under the DRPlus
Supplemental Cash Flow Information [Line Items]
Stock Issued	7	7
Union Electric Company
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures, including nuclear fuel expenditures	257	246
Net realized and unrealized gain – nuclear decommissioning trust fund	163	66
Return on investment in industrial development revenue bonds	0	240
Termination of a financing obligation	0	240
Union Electric Company | Issuance of common stock for stock-based compensation
Supplemental Cash Flow Information [Line Items]
Stock Issued	0	0
Union Electric Company | Issuance of common stock under the DRPlus
Supplemental Cash Flow Information [Line Items]
Stock Issued	0	0
Ameren Illinois Company
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures, including nuclear fuel expenditures	127	237
Net realized and unrealized gain – nuclear decommissioning trust fund	0	0
Return on investment in industrial development revenue bonds	0	0
Termination of a financing obligation	0	0
Ameren Illinois Company | Issuance of common stock for stock-based compensation
Supplemental Cash Flow Information [Line Items]
Stock Issued	0	0
Ameren Illinois Company | Issuance of common stock under the DRPlus
Supplemental Cash Flow Information [Line Items]
Stock Issued	$ 0	$ 0