Supplemental Income Statement Information (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Income Statement Information
Interest expense		$ 322	$ 199	$ 149
Interest income		(50)	(29)	(26)
Loss on extinguishment of debt	$ 96
Total		$ 272	$ 170	$ 123