Supplemental Information (Supplemental Cash Flow Information) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Supplemental Cash Flow Information [Line Items]
Wind generation expenditures	$ 0	$ 193
Accrued capital expenditures	345	271
Net realized and unrealized gain/(loss) – nuclear decommissioning trust fund	(71)	22
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	0	193
Accrued capital expenditures	194	141
Net realized and unrealized gain/(loss) – nuclear decommissioning trust fund	(71)	22
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	147	139
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