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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

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