CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating revenues
Contract drilling revenues	$ 626	$ 773	$ 1,935	$ 2,462
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	$ 398	$ 470	$ 1,267	$ 1,535
Cost, Product and Service [Extensible List]	us-gaap:OilAndGasServiceMember	us-gaap:OilAndGasServiceMember	us-gaap:OilAndGasServiceMember	us-gaap:OilAndGasServiceMember
Depreciation and amortization	$ 185	$ 190	$ 558	$ 592
General and administrative	40	45	118	133
Total costs and expenses	623	705	1,943	2,260
Loss on impairment				(597)
Loss on disposal of assets, net	(3)	(64)	(61)	(64)
Operating income (loss)		4	(69)	(459)
Other income (expense), net
Interest income	4	6	11	19
Interest expense, net of amounts capitalized	(110)	(145)	(340)	(458)
Gain on restructuring and retirement of debt		449	51	396
Other, net	3	21	26	(23)
Total other income (expense), net	(103)	331	(252)	(66)
Income (loss) before income tax expense (benefit)	(103)	335	(321)	(525)
Income tax expense (benefit)	27	(24)	10	4
Net income (loss)	(130)	359	(331)	(529)
Net income attributable to noncontrolling interest			1	1
Net income (loss) attributable to controlling interest	$ (130)	$ 359	$ (332)	$ (530)
Earnings (loss) per share, basic (in dollars per share)	$ (0.20)	$ 0.58	$ (0.53)	$ (0.86)
Earnings (loss) per share, diluted (in dollars per share)	$ (0.20)	$ 0.51	$ (0.53)	$ (0.86)
Weighted-average shares, basic (in shares)	653	616	630	615
Weighted-average shares, diluted (in shares)	653	702	630	615