CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Millions		Total		Common Stock	Preferred Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	Common Stock in Treasury
Balance beginning at Dec. 31, 2017		$ 1,979		$ 5		$ 4,698	$ (2,679)	$ (44)	$ (1)
Balance (in shares) at Dec. 31, 2017				512,134,311	1,725,000				31,269,000,000
Comprehensive income:
Net income		208					208
Comprehensive income		208
Stock-based compensation		7				7
Conversion of preferred stock (in shares)				74,998,614	(1,725,000)
Conversion of preferred stock				$ 1		(1)
Issuance of restricted stock (in shares)				5,076
Cancellation of restricted stock (in shares)				(160,168)
Performance units vested (in shares)				214,866
Tax withholding - stock compensation (in shares)				(338,808)
Tax withholding - stock compensation		(1)				(1)
Balance (in shares) at Mar. 31, 2018				586,853,891	0				31,269,000,000
Balance ending at Mar. 31, 2018		2,193		$ 6		4,703	(2,471)	(44)	$ (1)
Balance beginning at Dec. 31, 2017		1,979		$ 5		4,698	(2,679)	(44)	$ (1)
Balance (in shares) at Dec. 31, 2017				512,134,311	1,725,000				31,269,000,000
Comprehensive income:
Net income	[1]	259
Other comprehensive income		0
Comprehensive income	[1]	259
Balance (in shares) at Jun. 30, 2018				586,430,101	0				31,269,000,000
Balance ending at Jun. 30, 2018		2,250		$ 6		4,709	(2,420)	(44)	$ (1)
Balance beginning at Dec. 31, 2017		1,979		$ 5		4,698	(2,679)	(44)	$ (1)
Balance (in shares) at Dec. 31, 2017				512,134,311	1,725,000				31,269,000,000
Balance (in shares) at Dec. 31, 2018				585,407,107					39,092,537
Balance ending at Dec. 31, 2018		2,362		$ 6		4,715	(2,142)	(36)	$ (181)
Balance beginning at Mar. 31, 2018		2,193		$ 6		4,703	(2,471)	(44)	$ (1)
Balance (in shares) at Mar. 31, 2018				586,853,891	0				31,269,000,000
Comprehensive income:
Net income		51	[1]				51
Other comprehensive income		0
Comprehensive income	[1]	51
Stock-based compensation		6				6
Issuance of restricted stock (in shares)				307,743
Cancellation of restricted stock (in shares)				(722,465)
Tax withholding - stock compensation (in shares)				(9,068)
Balance (in shares) at Jun. 30, 2018				586,430,101	0				31,269,000,000
Balance ending at Jun. 30, 2018		$ 2,250		$ 6		4,709	(2,420)	(44)	$ (1)
Comprehensive income:
Treasury stock (in shares)		39,061,269
Treasury stock		$ (180)
Balance (in shares) at Dec. 31, 2018				585,407,107					39,092,537
Balance ending at Dec. 31, 2018		2,362		$ 6		4,715	(2,142)	(36)	$ (181)
Comprehensive income:
Net income		594					594
Comprehensive income		594
Stock-based compensation		$ 3				3
Issuance of restricted stock (in shares)				8,798
Cancellation of restricted stock (in shares)				(128,324)
Treasury stock (in shares)		5,260,687							5,260,687
Treasury stock		$ (21)							$ (21)
Performance units vested (in shares)				535,802
Tax withholding - stock compensation (in shares)				(274,657)
Tax withholding - stock compensation		(1)				(1)
Balance (in shares) at Mar. 31, 2019				585,548,726					44,353,224
Balance ending at Mar. 31, 2019		2,937		$ 6		4,717	(1,548)	(36)	$ (202)
Balance beginning at Dec. 31, 2018		2,362		$ 6		4,715	(2,142)	(36)	$ (181)
Balance (in shares) at Dec. 31, 2018				585,407,107					39,092,537
Comprehensive income:
Net income		732
Other comprehensive income		4						4
Comprehensive income		736
Balance (in shares) at Jun. 30, 2019				585,478,345					44,353,224
Balance ending at Jun. 30, 2019		3,082		$ 6		4,720	(1,410)	(32)	$ (202)
Balance beginning at Mar. 31, 2019		2,937		$ 6		4,717	(1,548)	(36)	$ (202)
Balance (in shares) at Mar. 31, 2019				585,548,726					44,353,224
Comprehensive income:
Net income		138					138
Other comprehensive income		4						4
Comprehensive income		142
Stock-based compensation		3				3
Issuance of restricted stock (in shares)				6,424
Cancellation of restricted stock (in shares)				(72,555)
Tax withholding - stock compensation (in shares)				(4,250)
Balance (in shares) at Jun. 30, 2019				585,478,345					44,353,224
Balance ending at Jun. 30, 2019		$ 3,082		$ 6		$ 4,720	$ (1,410)	$ (32)	$ (202)

[1] In 2018, deferred tax activity incurred in other comprehensive income was offset by a valuation allowance.