Supplemental Information (Supplemental Cash Flow Information) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures, including nuclear fuel expenditures	$ 381	$ 310
Net realized and unrealized gain/(loss) – nuclear decommissioning trust fund	(40)	74
Issuance of common stock for stock-based compensation
Supplemental Cash Flow Information [Line Items]
Stock Issued	25	16
Issuance of common stock under the DRPlus
Supplemental Cash Flow Information [Line Items]
Stock Issued	9	7
Union Electric Company
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures, including nuclear fuel expenditures	214	169
Net realized and unrealized gain/(loss) – nuclear decommissioning trust fund	(40)	74
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	159	122
Net realized and unrealized gain/(loss) – nuclear decommissioning trust fund	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