Supplemental Information (Leases) (Details) $ in Millions	Dec. 31, 2024 USD ($)
Schedule of Supplemental Balance Sheet Information Related to Operating Leases [Line Items]
Operating Lease, Right-of-Use Asset	$ 72
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Other assets
Operating Lease, Liability, Current	$ 5
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other current liabilities
Operating Lease, Liability, Noncurrent	$ 67
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other deferred credits and liabilities
Operating Lease, Weighted Average Remaining Lease Term	29 years
Operating Lease, Weighted Average Discount Rate, Percent	5.30%
Lessee, Operating Lease, Liability, to be Paid, Maturity [Line Items]
2025	$ 8
2026	5
2027	4
2028	4
2029	4
Thereafter	131
Total lease payments	156
Less imputed interest	84
Total	72
Ameren Missouri
Schedule of Supplemental Balance Sheet Information Related to Operating Leases [Line Items]
Operating Lease, Right-of-Use Asset	69
Operating Lease, Liability, Current	4
Operating Lease, Liability, Noncurrent	$ 65
Operating Lease, Weighted Average Remaining Lease Term	30 years
Operating Lease, Weighted Average Discount Rate, Percent	5.30%
Lessee, Operating Lease, Liability, to be Paid, Maturity [Line Items]
2025	$ 7
2026	4
2027	3
2028	4
2029	4
Thereafter	131
Total lease payments	153
Less imputed interest	84
Total	$ 69