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
Other comprehensive income	0
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
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
Other comprehensive income	0					0
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)