Inventory (Tables)

6 Months Ended

Jun. 30, 2018

Inventory Disclosure [Abstract]

Inventory Balance By Type

The following table summarizes the Company’s inventory balances as of the periods indicated (in millions):

	June 30, 2018		December 31, 2017
Fuel and other raw materials	$	293	$	284
Spare parts and supplies	290		278
Total	$	583	$	562