Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions		Total	Common Stock	Additional Paid in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings (Accumulated Deficit)
Beginning balance (in shares) at Dec. 31, 2017			57,321,228
Beginning balance at Dec. 31, 2017		$ 1,399	$ 1	$ 1,512	$ (16)	$ (98)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		35				35
Total other comprehensive income		(9)			(9)
Shares issued from Employee Stock Purchase Plan (in shares)			36,195
Shares issued from Employee Stock Purchase Plan		0
Reclassification of certain income tax effects	[1]				(5)	5
Stock-based compensation (in shares)			42,570
Stock-based compensation		2		2
Ending balance (in shares) at Mar. 31, 2018			57,399,993
Ending balance at Mar. 31, 2018		1,427	$ 1	1,514	(30)	(58)
Beginning balance (in shares) at Dec. 31, 2017			57,321,228
Beginning balance at Dec. 31, 2017		1,399	$ 1	1,512	(16)	(98)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		85
Ending balance (in shares) at Jun. 30, 2018			57,598,406
Ending balance at Jun. 30, 2018		1,475	$ 1	1,514	(32)	(8)
Beginning balance (in shares) at Mar. 31, 2018			57,399,993
Beginning balance at Mar. 31, 2018		1,427	$ 1	1,514	(30)	(58)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		50				50
Total other comprehensive income		(2)			(2)
Shares issued from Employee Stock Purchase Plan (in shares)			28,748
Shares issued from Employee Stock Purchase Plan		0
Stock-based compensation (in shares)			169,665
Stock-based compensation		0
Ending balance (in shares) at Jun. 30, 2018			57,598,406
Ending balance at Jun. 30, 2018		1,475	$ 1	1,514	(32)	(8)
Beginning balance (in shares) at Dec. 31, 2018			57,749,464
Beginning balance at Dec. 31, 2018		1,570	$ 1	1,522	(47)	94
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		36				36
Total other comprehensive income		16			16
Shares issued from Employee Stock Purchase Plan (in shares)			32,878
Shares issued from Employee Stock Purchase Plan		0
Stock-based compensation (in shares)			27,401
Stock-based compensation		4		4
Dividends declared and paid		(2)				(2)
Repurchase of shares (in shares)	[2]		(1,329,657)
Repurchase of shares	[2]	(50)		(50)
Ending balance (in shares) at Mar. 31, 2019			56,480,086
Ending balance at Mar. 31, 2019		1,574	$ 1	1,476	(31)	128
Beginning balance (in shares) at Dec. 31, 2018			57,749,464
Beginning balance at Dec. 31, 2018		1,570	$ 1	1,522	(47)	94
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		97
Ending balance (in shares) at Jun. 30, 2019			56,483,937
Ending balance at Jun. 30, 2019		1,656	$ 1	1,477	(8)	186
Beginning balance (in shares) at Mar. 31, 2019			56,480,086
Beginning balance at Mar. 31, 2019		1,574	$ 1	1,476	(31)	128
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income		61				61
Total other comprehensive income		23			23
Shares issued from Employee Stock Purchase Plan (in shares)			26,785
Shares issued from Employee Stock Purchase Plan		0
Stock-based compensation (in shares)			164,926
Stock-based compensation		1		1
Dividends declared and paid (in shares)	[2]		188
Dividends declared and paid	[2]	(3)				(3)
Repurchase of shares (in shares)	[3]		(188,048)
Repurchase of shares	[3]	0
Ending balance (in shares) at Jun. 30, 2019			56,483,937
Ending balance at Jun. 30, 2019		$ 1,656	$ 1	$ 1,477	$ (8)	$ 186

[1] Income tax effects of the Tax Cuts and Jobs Act are reclassified from AOCI to retained earnings due to the adoption of ASU 2018-02.

[2] Includes dividend reinvestment shares.

[3] For further information, see Item 2. Unregistered Sales of Equity Securities and Use of Proceeds.