CONSOLIDATED STATEMENT OF STOCKHOLDERS’ EQUITY - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive 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)	77				77
Other comprehensive income, net	1			1
Ending Balance (in shares) at Mar. 31, 2017		57.0
Ending Balance at Mar. 31, 2017	$ 1,727	$ 0	841	(1)	887
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)	(250)
Conversion of 1.625% Notes	0
Other comprehensive income, net	1
Ending Balance (in shares) at Sep. 30, 2017		57.0
Ending Balance at Sep. 30, 2017	1,429	$ 0	870	(1)	560
Beginning Balance (in shares) at Mar. 31, 2017		57.0
Beginning Balance at Mar. 31, 2017	1,727	$ 0	841	(1)	887
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(230)				(230)
Share-based compensation	$ 24		24
Ending Balance (in shares) at Jun. 30, 2017	56.5	57.0
Ending Balance at Jun. 30, 2017	$ 1,521	$ 0	865	(1)	657
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(97)				(97)
Other comprehensive income, net	0
Share-based compensation	5		5
Ending Balance (in shares) at Sep. 30, 2017		57.0
Ending Balance at Sep. 30, 2017	1,429	$ 0	870	(1)	560
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of ASU \| Topic 606	6				6
Adoption of ASU \| ASU 2018-02	$ 0			(1)	1
Beginning Balance (in shares) at Dec. 31, 2017	59.3	60.0
Beginning Balance at Dec. 31, 2017	$ 1,337	$ 0	1,044	(5)	298
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	107				107
Exchange of 1.625% Notes (in shares)		2.0
Conversion of 1.625% Notes	108		108
Other comprehensive income, net	(6)			(6)
Share-based compensation	1		1
Ending Balance (in shares) at Mar. 31, 2018		62.0
Ending Balance at Mar. 31, 2018	$ 1,553	$ 0	1,153	(12)	412
Beginning Balance (in shares) at Dec. 31, 2017	59.3	60.0
Beginning Balance at Dec. 31, 2017	$ 1,337	$ 0	1,044	(5)	298
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	506
Conversion of 1.625% Notes	108
Other comprehensive income, net	(4)
Ending Balance (in shares) at Sep. 30, 2018		62.0
Ending Balance at Sep. 30, 2018	1,561	$ 0	760	(10)	811
Beginning Balance (in shares) at Mar. 31, 2018		62.0
Beginning Balance at Mar. 31, 2018	1,553	$ 0	1,153	(12)	412
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	202				202
Partial termination of 1.125% Warrants	(113)		(113)		0
Other comprehensive income, net	1			1
Share-based compensation	$ 15		15
Ending Balance (in shares) at Jun. 30, 2018	61.3	62.0
Ending Balance at Jun. 30, 2018	$ 1,658	$ 0	1,055	(11)	614
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	197				197
Partial termination of 1.125% Warrants	(306)		(306)		0
Conversion of 1.625% Notes	4		4
Other comprehensive income, net	1			1
Share-based compensation	7		7
Ending Balance (in shares) at Sep. 30, 2018		62.0
Ending Balance at Sep. 30, 2018	$ 1,561	$ 0	$ 760	$ (10)	$ 811

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