Statement of Changes in Equity (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ 636,176	$ 1,881,701	$ 992,461	$ 2,608,727
Shares issued under stock-based compensation plans	50	603	164	2,093
Stock-based compensation expense	52,739	46,631	145,920	121,405
Temporary equity reclassification	8,796		(19,286)	79,494
Common stock issued under employee stock purchase plan	16,004	25,433	33,462	25,433
Stock repurchases, net	(116,175)	(74,956)	(881,154)	(574,957)
Restricted shares turned in for tax withholding	(3,654)	(10,633)	(53,589)	(71,179)
Other comprehensive income, net of tax	427	112	(7,485)	6,637
Cumulative-effect adjustment from adoption of accounting standards			132,778	388
Distribution of the net assets of the GoTo Business				(464,752)
Other				(848)
Net income	158,857	126,720	409,949	263,170
Ending balance	$ 753,220	$ 1,995,611	$ 753,220	$ 1,995,611
Beginning balance, treasury shares (in shares)			(162,044,000)
Restricted shares turned in for tax withholding (in shares)	(32,813)	(135,003)	(570,589)	(870,656)
Ending balance, treasury shares (in shares)	(173,322,000)		(173,322,000)
Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	307,662,000	304,891,000	305,751,000	302,851,000
Shares issued under stock compensation plans (shares)	110,000	259,000	1,769,000	2,299,000
Common stock issued under employee stock purchase plan (shares)	209,000	286,000	461,000	286,000
Ending balance (in shares)	307,981,000	305,436,000	307,981,000	305,436,000
Beginning balance	$ 308	$ 305	$ 306	$ 303
Shares issued under stock-based compensation plans			2	2
Ending balance	308	305	308	305
Additional Paid-in Capital [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	5,116,339	4,922,187	4,883,670	4,761,588
Shares issued under stock-based compensation plans	50	603	162	2,091
Stock-based compensation expense	52,739	46,631	145,920	121,405
Temporary equity reclassification	8,796		(19,286)	79,494
Common stock issued under employee stock purchase plan	16,004	25,433	33,462	25,433
Stock repurchases, net			150,000
Cumulative-effect adjustment from adoption of accounting standards				5,691
Other				(848)
Ending balance	5,193,928	4,994,854	5,193,928	4,994,854
Retained Earnings [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	3,893,354	3,663,732	3,509,484	4,010,737
Cumulative-effect adjustment from adoption of accounting standards			132,778	(5,303)
Distribution of the net assets of the GoTo Business				(478,152)
Net income	158,857	126,720	409,949	263,170
Ending balance	4,052,211	3,790,452	4,052,211	3,790,452
Accumulated Other Comprehensive (Loss) Income [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(18,718)	(8,779)	(10,806)	(28,704)
Other comprehensive income, net of tax	427	112	(7,485)	6,637
Distribution of the net assets of the GoTo Business				13,400
Ending balance	(18,291)	(8,667)	(18,291)	(8,667)
Treasury Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(8,355,107)	(6,695,744)	(7,390,193)	(6,135,197)
Stock repurchases, net	(116,175)	(74,956)	(1,031,154)	(574,957)
Restricted shares turned in for tax withholding	(3,654)	(10,633)	(53,589)	(71,179)
Ending balance	$ (8,474,936)	$ (6,781,333)	$ (8,474,936)	$ (6,781,333)
Beginning balance, treasury shares (in shares)	(172,244,000)	(153,687,000)	(162,044,000)	(146,552,000)
Stock repurchases net (shares)	(1,046,000)	(985,000)	(10,708,000)	(7,384,000)
Restricted shares turned in for tax withholding (in shares)	(32,000)	(135,000)	(570,000)	(871,000)
Ending balance, treasury shares (in shares)	(173,322,000)	(154,807,000)	(173,322,000)	(154,807,000)