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Supplemental Information (Inventories) (Details) - USD ($) $ in Millions | Dec. 31, 2025 | Dec. 31, 2024
--- | --- | ---
Public Utilities, Inventory [Line Items] |  |
Fuel | $ 101 | $ 113
Natural gas stored underground | 98 | 91
Materials, supplies, and other | 575 | 558
Total inventories | 774 | 762
Ameren Missouri |  |
Public Utilities, Inventory [Line Items] |  |
Fuel | 101 | 113
Natural gas stored underground | 10 | 9
Materials, supplies, and other | 381 | 392
Total inventories | 492 | 514
Ameren Illinois |  |
Public Utilities, Inventory [Line Items] |  |
Fuel | 0 | 0
Natural gas stored underground | 88 | 82
Materials, supplies, and other | 190 | 162
Total inventories | $ 278 | $ 244

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