Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Supplemental Cash Flow Information [Abstract]
Interest paid, net of amounts capitalized	$ 120	$ 118	$ 133
Taxes paid, net of refunds	167	157	100
Noncash Investing and Financing Activities
Accrued treasury stock repurchases	0	4	13
Accrued capital expenditures	(16)	20	(4)
Asset retirement obligations	5	6	(7)
ROU assets obtained in exchange for finance lease liabilities	$ 78	$ 0	$ 0