CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Operating revenues
Revenues	$ 773	$ 784	$ 2,462	$ 2,296
Revenue from Contract with Customer, Product and Service [Extensible List]	us-gaap:OilAndGasServiceMember	us-gaap:OilAndGasServiceMember	us-gaap:OilAndGasServiceMember	us-gaap:OilAndGasServiceMember
Costs and expenses
Operating and maintenance	$ 470	$ 547	$ 1,535	$ 1,565
Cost, Product and Service [Extensible List]	us-gaap:OilAndGasServiceMember	us-gaap:OilAndGasServiceMember	us-gaap:OilAndGasServiceMember	us-gaap:OilAndGasServiceMember
Depreciation and amortization	$ 190	$ 212	$ 592	$ 648
General and administrative	45	45	133	139
Total costs and expenses	705	804	2,260	2,352
Loss on impairment		583	597	584
Loss on disposal of assets, net	(64)	(4)	(64)	(7)
Operating income (loss)	4	(607)	(459)	(647)
Other income (expense), net
Interest income	6	11	19	33
Interest expense, net of amounts capitalized	(145)	(166)	(458)	(500)
Gain (loss) on restructuring and retirement of debt	449	(12)	396	(39)
Other, net	21	3	(23)	34
Total other income (expense), net	331	(164)	(66)	(472)
Income (loss) before income tax expense	335	(771)	(525)	(1,119)
Income tax expense (benefit)	(24)	54	4	83
Net income (loss)	359	(825)	(529)	(1,202)
Net income attributable to noncontrolling interest			1	2
Net income (loss) attributable to controlling interest	$ 359	$ (825)	$ (530)	$ (1,204)
Earnings (loss) per share
Basic (in dollars per share)	$ 0.58	$ (1.35)	$ (0.86)	$ (1.97)
Diluted (in dollars per share)	$ 0.51	$ (1.35)	$ (0.86)	$ (1.97)
Weighted-average shares outstanding
Basic (in shares)	616	613	615	612
Diluted (in shares)	702	613	615	612