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Supplemental Information (Inventories) (Details) - USD ($) $ in Millions | Dec. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Public Utilities, Inventory [Line Items] |  |
Fuel | $ 109 | $ 79
Natural gas stored underground | 95 | 130
Materials, supplies, and other | 529 | 458
Total inventories | 733 | 667
Ameren Missouri |  |
Public Utilities, Inventory [Line Items] |  |
Fuel | 109 | 79
Natural gas stored underground | 8 | 10
Materials, supplies, and other | 391 | 345
Total inventories | 508 | 434
Ameren Illinois |  |
Public Utilities, Inventory [Line Items] |  |
Fuel | 0 | 0
Natural gas stored underground | 87 | 120
Materials, supplies, and other | 138 | 113
Total inventories | $ 225 | $ 233

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