CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Millions		Total		Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Common Stock in Treasury
Balance (in shares) at Dec. 31, 2019				585,555,923				44,353,224
Balance beginning at Dec. 31, 2019		$ 3,246		$ 6	$ 4,726	$ (1,251)	$ (33)	$ (202)
Comprehensive income (loss):
Net (loss) income		(1,547)				(1,547)
Comprehensive income (loss)		(1,547)
Stock-based compensation		1			1
Issuance of restricted stock (in shares)				12,397
Cancellation of restricted stock (in shares)				(167,130)
Restricted units granted (in shares)				1,005,976
Restricted units granted		1			1
Tax withholding - stock compensation (in shares)				(383,731)
Balance (in shares) at Mar. 31, 2020				586,023,435				44,353,224
Balance ending at Mar. 31, 2020		1,701		$ 6	4,728	(2,798)	(33)	$ (202)
Balance (in shares) at Dec. 31, 2019				585,555,923				44,353,224
Balance beginning at Dec. 31, 2019		3,246		$ 6	4,726	(1,251)	(33)	$ (202)
Comprehensive income (loss):
Net (loss) income		(2,427)
Other comprehensive income	[1]	0
Comprehensive income (loss)		(2,427)
Balance (in shares) at Jun. 30, 2020				586,593,540				44,353,224
Balance ending at Jun. 30, 2020		823		$ 6	4,730	(3,678)	(33)	$ (202)
Balance (in shares) at Mar. 31, 2020				586,023,435				44,353,224
Balance beginning at Mar. 31, 2020		1,701		$ 6	4,728	(2,798)	(33)	$ (202)
Comprehensive income (loss):
Net (loss) income		(880)				(880)
Other comprehensive income	[1]	0
Comprehensive income (loss)		(880)
Stock-based compensation		1			1
Issuance of restricted stock (in shares)				222,489
Cancellation of restricted stock (in shares)				(1,079,515)
Restricted units granted (in shares)				1,649,294
Restricted units granted		2			2
Tax withholding - stock compensation (in shares)				(222,163)
Tax withholding – stock compensation		(1)			(1)
Balance (in shares) at Jun. 30, 2020				586,593,540				44,353,224
Balance ending at Jun. 30, 2020		823		$ 6	4,730	(3,678)	(33)	$ (202)
Balance (in shares) at Dec. 31, 2020				718,795,700				44,353,224
Balance beginning at Dec. 31, 2020		497		$ 7	5,093	(4,363)	(38)	$ (202)
Comprehensive income (loss):
Net (loss) income		80				80
Comprehensive income (loss)		80
Issuance of restricted stock (in shares)				10,067
Cancellation of restricted stock (in shares)				(405)
Restricted units granted (in shares)				2,136,882
Restricted units granted		8			8
Performance units vested (in shares)				1,001,505
Performance units vested		4			4
Tax withholding - stock compensation (in shares)				(748,627)
Tax withholding – stock compensation		(3)			(3)
Balance (in shares) at Mar. 31, 2021				721,195,122				44,353,224
Balance ending at Mar. 31, 2021		586		$ 7	5,102	(4,283)	(38)	$ (202)
Balance (in shares) at Dec. 31, 2020				718,795,700				44,353,224
Balance beginning at Dec. 31, 2020		497		$ 7	5,093	(4,363)	(38)	$ (202)
Comprehensive income (loss):
Net (loss) income		(529)
Other comprehensive income	[1]	3
Comprehensive income (loss)		(526)
Balance (in shares) at Jun. 30, 2021				721,372,443				44,353,224
Balance ending at Jun. 30, 2021		(18)		$ 7	5,104	(4,892)	(35)	$ (202)
Balance (in shares) at Mar. 31, 2021				721,195,122				44,353,224
Balance beginning at Mar. 31, 2021		586		$ 7	5,102	(4,283)	(38)	$ (202)
Comprehensive income (loss):
Net (loss) income		(609)				(609)
Other comprehensive income		3	[1]				3
Comprehensive income (loss)		(606)
Stock-based compensation		2			2
Issuance of restricted stock (in shares)				148,700
Restricted units granted (in shares)				41,879
Tax withholding - stock compensation (in shares)				(13,258)
Balance (in shares) at Jun. 30, 2021				721,372,443				44,353,224
Balance ending at Jun. 30, 2021		$ (18)		$ 7	$ 5,104	$ (4,892)	$ (35)	$ (202)

[1] Net of $1 million tax benefits for the three and six months ended June 30, 2021 and for the six months ended June 30, 2020. Tax benefits for the three months ended June 30, 2020 were immaterial.