Supplemental Information (Supplemental Cash Flow Information) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Supplemental Cash Flow Information [Line Items]
Wind generation expenditures	$ 224		$ 417
Accrued capital expenditures		$ 408	434
Net realized and unrealized gain/(loss) – nuclear decommissioning trust fund		(211)	85
Issuance of common stock for stock-based compensation
Supplemental Cash Flow Information [Line Items]
Stock Issued		31	33
Issuance of common stock under the DRPlus
Supplemental Cash Flow Information [Line Items]
Stock Issued		8	0
Union Electric Company
Supplemental Cash Flow Information [Line Items]
Wind generation expenditures	$ 224		417
Accrued capital expenditures		204	259
Net realized and unrealized gain/(loss) – nuclear decommissioning trust fund		(211)	85
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		193	174
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