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Supplemental Information (Inventories) (Details) - USD ($) $ in Millions | Dec. 31, 2022 | Dec. 31, 2021
--- | --- | ---
Public Utilities, Inventory [Line Items] |  |
Fuel | $ 79 | $ 118
Natural gas stored underground | 130 | 99
Materials, supplies, and other | 458 | 375
Total inventories | 667 | 592
Union Electric Company |  |
Public Utilities, Inventory [Line Items] |  |
Fuel | 79 | 118
Natural gas stored underground | 10 | 9
Materials, supplies, and other | 345 | 292
Total inventories | 434 | 419
Ameren Illinois Company |  |
Public Utilities, Inventory [Line Items] |  |
Fuel | 0 | 0
Natural gas stored underground | 120 | 90
Materials, supplies, and other | 113 | 83
Total inventories | $ 233 | $ 173

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