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Inventory
6 Months Ended
Jun. 30, 2021
Inventory Disclosure [Abstract]  
INVENTORY INVENTORY
The following table summarizes the Company’s inventory balances as of the periods indicated (in millions):
June 30, 2021December 31, 2020
Fuel and other raw materials$228 $223 
Spare parts and supplies217 238 
Total$445 $461