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MATERIALS, SUPPLIES, AND INVENTORIES
 9 Months Ended
Sep. 30, 2021
Inventory Disclosure [Abstract]  
MATERIALS, SUPPLIES, AND INVENTORIES MATERIALS, SUPPLIES, AND INVENTORIES
Our inventory consisted of:
(in millions)September 30, 2021December 31, 2020
Materials and supplies$141.3 $136.5 
Natural gas in storage49.0 25.9 
Fossil fuel35.8 57.1 
Total$226.1 $219.5 

Substantially all materials and supplies, natural gas in storage, and fossil fuel inventories are recorded using the weighted-average cost method of accounting.