Summary Of Significant Accounting Policies - Schedule of Other Assets and Other Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Accounting Policies [Line Items]
Unbilled revenue	$ 413	$ 346
Other current assets	252	162
Regulatory Asset	2,611	2,397
Current maturities of long-term debt	29	317
Interest accrued	183	196
Current regulatory liabilities	142	120
Long-term debt, net	19,172	17,262
Ameren Missouri Securitization Funding I, LLC
Accounting Policies [Line Items]
Unbilled revenue	4	0
Other current assets	46	2
Regulatory Asset	449	465
Current maturities of long-term debt	29	17
Interest accrued	18	1
Current regulatory liabilities	15	0
Long-term debt, net	$ 437	$ 448