Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Net cash used in operating activities:
Interest paid, net of amounts capitalized	$ (187)	$ (269)
Income taxes paid to taxing authorities	(298)	(101)
Noncash investing activities, related to continuing operations:
Increase (decrease) in asset retirement costs	12	(94)
Asset retirement obligations assumed by buyer	82	14
Notes receivable for disposal of assets	0	745
Capital expenditures incurred but not yet paid	$ 238	$ 361