Supplementary Information - Consolidated Statements of Cash Flow (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplementary Cash Flow Information
Share-based compensation expense	$ 26	$ 28	$ 21
Other	13	16	18
Total other non-cash charges to net income	39	44	39
Interest paid	77	59	52
Income taxes paid	$ 289	$ 254	$ 158