Supplemental Disclosures of Cash Flow (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Disclosures of Cash Flow Data [Abstract]
Interest paid	$ 248	$ 274	$ 265
Income taxes paid (received)	$ 170	$ 197	215
Significant non-cash investing and financing transactions:
Other assets received in our financing transaction			$ 252