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MATERIALS, SUPPLIES, AND INVENTORIES (Details) - USD ($)
$ in Millions
Mar. 31, 2024
Dec. 31, 2023
Energy Related Inventory    
Materials and supplies $ 330.5 $ 320.0
Natural gas in storage 160.0 327.8
Fossil fuel 118.1 127.4
Total 608.6 $ 775.2
LIFO Method Related Items    
LIFO liquidation debit $ 4.3