Other Income, Net (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other Income and Expenses [Abstract]
Interest income	$ 19	$ 8	$ 6
Other nonoperating income	7	3	4
Insurance policy expense	(3)	(3)	(4)
Other income, net	$ 23	$ 8	$ 6