Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019
Included in operating activities:
Interest paid, net of amounts capitalized		$ 175	$ 177
Income taxes paid to (received from) taxing authorities, net of refunds		(50)	67
Noncash investing activities:
Increase (decrease) in asset retirement costs		(5)	40
Asset retirement obligations assumed by buyer		0	1,082
Proceeds from income tax refunds	$ 89	94	89
Capital expenditures incurred but not yet paid		$ 81	$ 302