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Inventory (Tables)
3 Months Ended
Mar. 31, 2021
Inventory Disclosure [Abstract]  
Inventory Balance By Type
The following table summarizes the Company’s inventory balances as of the periods indicated (in millions):
March 31, 2021December 31, 2020
Fuel and other raw materials$214 $223 
Spare parts and supplies232 238 
Total$446 $461