Supplemental Information (Supplemental Cash Flow Information) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures	$ 622	$ 480	$ 518
Net realized and unrealized gain (loss) – nuclear decommissioning trust fund	160	165	167
Return on investment in industrial development revenue bonds	0	0	240
Stock Issued		16
Termination of a financing obligation	0	0	240
Ameren (parent)
Supplemental Cash Flow Information [Line Items]
Stock Issued	25	16	40
Issuance of common stock for stock-based compensation
Supplemental Cash Flow Information [Line Items]
Stock Issued	25	16	40
Issuance of common stock under the DRPlus \| Ameren (parent)
Supplemental Cash Flow Information [Line Items]
Stock Issued	7	7	7
Ameren Missouri
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures	355	303	270
Net realized and unrealized gain (loss) – nuclear decommissioning trust fund	160	165	167
Return on investment in industrial development revenue bonds	0	0	240
Termination of a financing obligation	0	0	240
Ameren Missouri \| Issuance of common stock for stock-based compensation
Supplemental Cash Flow Information [Line Items]
Stock Issued	0	0	0
Ameren Missouri \| Issuance of common stock under the DRPlus
Supplemental Cash Flow Information [Line Items]
Stock Issued	0	0	0
Ameren Illinois
Supplemental Cash Flow Information [Line Items]
Accrued capital expenditures	210	157	212
Net realized and unrealized gain (loss) – nuclear decommissioning trust fund	0	0	0
Return on investment in industrial development revenue bonds	0	0	0
Termination of a financing obligation	0	0	0
Ameren Illinois \| Issuance of common stock for stock-based compensation
Supplemental Cash Flow Information [Line Items]
Stock Issued	0	0	0
Ameren Illinois \| Issuance of common stock under the DRPlus
Supplemental Cash Flow Information [Line Items]
Stock Issued	$ 0	$ 0	$ 0

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