Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings
Beginning Balance (in shares) at Dec. 31, 2016	55.8	57.0
Beginning Balance at Dec. 31, 2016	$ 1,649	$ 0	$ 841	$ (2)	$ 810
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(512)				(512)
Exchange of convertible senior notes (in shares)		3.0
Exchange of convertible senior notes	161		161
Other comprehensive income (loss), net	(3)			(3)
Share-based compensation	$ 42		42
Ending Balance (in 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]
Net income (loss)	707				707
Exchange of convertible senior notes (in shares)		2.0
Exchange of convertible senior notes	108		108
Other comprehensive income (loss), net	(2)			(2)
Share-based compensation	37		37
Partial termination of warrants	(550)		(550)
Conversion of convertible senior notes	$ 4		4
Ending Balance (in shares) at Dec. 31, 2018	62.1	62.0
Ending Balance at Dec. 31, 2018	$ 1,647	$ 0	643	(8)	1,012
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	737				737
Common stock purchases	(54)	$ (54)	(1)		(53)
Exchange of convertible senior notes	0
Other comprehensive income (loss), net	12			12
Share-based compensation	47		47
Partial termination of warrants	(514)		(514)
Ending Balance (in shares) at Dec. 31, 2019		62.0
Ending Balance at Dec. 31, 2019	$ 1,960	$ 0	$ 175	$ 4	$ 1,781