Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Cash Flow Information [Abstract]
Interest paid, net of amounts capitalized	$ 130	$ 130	$ 120
Taxes paid, net of refunds	123	129	151
Noncash Investing and Financing Activities
Accrued capital expenditures	14	1	(37)
Asset retirement obligations	2	2	3
Capital lease obligations	0	0	6
Fair value adjustment to securities available for sale, net of tax	(1)	0
Distribution to noncontrolling interests (Note 5)	$ 0	$ 0	$ (4)