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Supplemental Information (Inventories) (Details) - USD ($) $ in Millions | Dec. 31, 2024 | Dec. 31, 2023
--- | --- | ---
Public Utilities, Inventory [Line Items] |  |
Fuel | $ 113 | $ 109
Natural gas stored underground | 91 | 95
Materials, supplies, and other | 558 | 529
Total inventories | 762 | 733
Ameren Missouri |  |
Public Utilities, Inventory [Line Items] |  |
Fuel | 113 | 109
Natural gas stored underground | 9 | 8
Materials, supplies, and other | 392 | 391
Total inventories | 514 | 508
Ameren Illinois |  |
Public Utilities, Inventory [Line Items] |  |
Fuel | 0 | 0
Natural gas stored underground | 82 | 87
Materials, supplies, and other | 162 | 138
Total inventories | $ 244 | $ 225

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