Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental Cash Flow Information [Abstract]
Interest paid, net of amounts capitalized	$ 133	$ 130	$ 130
Taxes paid, net of refunds	100	123	129
Noncash Investing and Financing Activities
Accrued treasury stock repurchases	13	0	0
Accrued capital expenditures	(4)	14	1
Asset retirement obligations	(7)	(2)	(2)
Fair value adjustment to securities available for sale, net of tax	$ 0	$ (1)	$ 0