Supplemental Information (Supplemental Cash Flow Information) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures, including nuclear fuel expenditures	$ 453	$ 380
Net realized and unrealized gain – nuclear decommissioning trust fund	57	103
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	7	7
Union Electric Company
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures, including nuclear fuel expenditures	284	232
Net realized and unrealized gain – nuclear decommissioning trust fund	57	103
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	162	134
Net realized and unrealized gain – 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