Condensed Consolidated Statement of Changes in Stockholders' Equity - USD ($) $ in Millions	Total	Class B Common Stock	Common Stock	Common Stock Class B Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Beginning balance at Dec. 31, 2017	$ 1,363				$ 926	$ 926	$ (42)	$ (447)
Beginning balance, shares at Dec. 31, 2017			135,617,263	12,799,999				(9,474,490)
Net income	36					36
Cumulative effect adjustment from adoption of new accounting guidance	4					4
Other comprehensive loss	(9)						(9)
Issuance of common stock related to exercises of options and vesting of RSUs	3				3
Issuance of common stock related to exercises of options and vesting of RSUs, shares			1,160,769
Repurchase of common stock (Note 13)	$ (100)							$ (100)
Repurchase of common stock, shares	(2,582,198)							(2,582,198)
Withholding taxes on net share settlements of equity awards	$ (18)				(18)
Stock-based compensation	68				68
Ending balance at Jun. 30, 2018	1,347				979	966	(51)	$ (547)
Ending balance, shares at Jun. 30, 2018			136,778,032	12,799,999				(12,056,688)
Beginning balance at Mar. 31, 2018	1,389				946	934	(34)	$ (457)
Beginning balance, shares at Mar. 31, 2018			136,396,872	12,799,999				(9,727,140)
Net income	32					32
Other comprehensive loss	(17)						(17)
Issuance of common stock related to exercises of options and vesting of RSUs	3				3
Issuance of common stock related to exercises of options and vesting of RSUs, shares			381,160
Repurchase of common stock (Note 13)	$ (90)							$ (90)
Repurchase of common stock, shares	(2,329,548)							(2,329,548)
Withholding taxes on net share settlements of equity awards	$ (6)				(6)
Stock-based compensation	36				36
Ending balance at Jun. 30, 2018	1,347				979	966	(51)	$ (547)
Ending balance, shares at Jun. 30, 2018			136,778,032	12,799,999				(12,056,688)
Beginning balance at Dec. 31, 2018	$ 1,471				1,037	1,043	(62)	$ (547)
Beginning balance, shares at Dec. 31, 2018	125,101,322	12,799,999	137,158,010	12,799,999				(12,056,688)
Net income	$ 60					60
Cumulative effect adjustment from adoption of new accounting guidance	3					3
Other comprehensive loss	(3)						(3)
Issuance of common stock related to exercises of options and vesting of RSUs	$ 1				1
Issuance of common stock related to exercises of options and vesting of RSUs, shares			1,367,148
Repurchase of common stock, shares	0
Withholding taxes on net share settlements of equity awards	$ (26)				(26)
Stock-based compensation	69				69
Ending balance at Jun. 30, 2019	$ 1,575				1,081	1,106	(65)	$ (547)
Ending balance, shares at Jun. 30, 2019	126,468,470	12,799,999	138,525,158	12,799,999				(12,056,688)
Beginning balance at Mar. 31, 2019	$ 1,507				1,046	1,072	(64)	$ (547)
Beginning balance, shares at Mar. 31, 2019			138,256,630	12,799,999				(12,056,688)
Net income	34					34
Other comprehensive loss	(1)						(1)
Issuance of common stock related to exercises of options and vesting of RSUs	$ 1				1
Issuance of common stock related to exercises of options and vesting of RSUs, shares			268,528
Repurchase of common stock, shares	0
Withholding taxes on net share settlements of equity awards	$ (4)				(4)
Stock-based compensation	38				38
Ending balance at Jun. 30, 2019	$ 1,575				$ 1,081	$ 1,106	$ (65)	$ (547)
Ending balance, shares at Jun. 30, 2019	126,468,470	12,799,999	138,525,158	12,799,999				(12,056,688)