Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Retained Earnings
Beginning Balance, shares at Dec. 31, 2015	55.1	56.0
Beginning Balance at Dec. 31, 2015	$ 1,557	$ 0	$ 803	$ (4)	$ 758
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	52				52
Other comprehensive income (loss), net	2			2
Share-based compensation, shares		1.0
Share-based compensation	36		36
Tax benefit from share-based compensation	2		2
Exchange of 1.625% Convertible Notes	$ 0
Ending Balance, shares at Dec. 31, 2016	55.8	57.0
Ending Balance at Dec. 31, 2016	$ 1,649	$ 0	841	(2)	810
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(512)				(512)
Other comprehensive income (loss), net	(3)			(3)
Share-based compensation	42		42
Exchange of 1.625% Convertible Notes, shares		3.0
Exchange of 1.625% Convertible Notes	$ 161		161
Ending Balance, shares at Dec. 31, 2017	59.3	60.0
Ending Balance at Dec. 31, 2017	$ 1,337	$ 0	1,044	(5)	298
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of ASU | Adoption of Topic 606	6				6
Adoption of ASU | Adoption of ASU 2018-02	0			(1)	1
Net income (loss)	707
Other comprehensive income (loss), net	(2)			(2)
Share-based compensation	37		37
Exchange of 1.625% Convertible Notes, shares		2.0
Exchange of 1.625% Convertible Notes	108		108
Partial termination of 1.125% Warrants	(550)		(550)
Conversion of 1.625% Convertible Notes	4		4
Ending Balance, shares at Dec. 31, 2018		62.0
Ending Balance at Dec. 31, 2018	$ 1,647	$ 0	$ 643	$ (8)	$ 1,012