Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Cash Flow Elements [Abstract]
Cash paid for income taxes, net of refunds	$ 176	$ 121	$ 20
Cash paid for interest	$ 145	209	$ 193
Non-cash purchase price consideration		$ 89