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Inventory
9 Months Ended
Sep. 30, 2018
Inventory Disclosure [Abstract]  
INVENTORY INVENTORY
The following table summarizes the Company’s inventory balances as of the periods indicated (in millions):
 
September 30, 2018
 
December 31, 2017
Fuel and other raw materials
$
278

 
$
284

Spare parts and supplies
284

 
278

Total
$
562

 
$
562