Supplemental Information (Leases) (Details) $ in Millions	Sep. 30, 2024 USD ($)
Schedule of Supplemental Balance Sheet Information Related to Operating Leases [Line Items]
Operating Lease, Right-of-Use Asset	$ 38
Operating Lease, Liability, Current	6
Operating Lease, Liability, Noncurrent	$ 32
Operating Lease, Weighted Average Remaining Lease Term	23 years
Operating Lease, Weighted Average Discount Rate, Percent	5.40%
Lessee, Operating Lease, Liability, to be Paid, Maturity [Line Items]
2024	$ 2
2025	6
2026	3
2027	2
2028	2
Thereafter	55
Total lease payments	70
Less imputed interest	32
Total	38
Union Electric Company
Schedule of Supplemental Balance Sheet Information Related to Operating Leases [Line Items]
Operating Lease, Right-of-Use Asset	35
Operating Lease, Liability, Current	5
Operating Lease, Liability, Noncurrent	$ 30
Operating Lease, Weighted Average Remaining Lease Term	24 years
Operating Lease, Weighted Average Discount Rate, Percent	5.40%
Lessee, Operating Lease, Liability, to be Paid, Maturity [Line Items]
2024	$ 2
2025	5
2026	2
2027	2
2028	2
Thereafter	53
Total lease payments	66
Less imputed interest	31
Total	$ 35