Consolidated Statements Of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (loss)
Beginning balances (shares) at Dec. 31, 2013		38.2
Beginning balance at Dec. 31, 2013	$ 3,501.4	$ 0.0	$ 2,519.9	$ 979.4	$ 2.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options and under stock purchase plan (in shares)		0.9
Issuance of common stock through employee stock plans	283.6		283.6
Income tax benefit from employee stock plans	13.9		13.9
Share-based compensation expense related to employee stock plans	168.9		168.9
Repurchase and retirement of common stock (in shares)		(2.5)
Repurchase and retirement of common stock	(1,000.0)		(89.5)	(910.5)
Net income	418.8			418.8
Other comprehensive loss	(7.2)				(7.2)
Ending balances (shares) at Dec. 31, 2014		36.6
Ending balance at Dec. 31, 2014	3,379.4	$ 0.0	2,896.8	487.7	(5.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options and under stock purchase plan (in shares)		1.2
Issuance of common stock through employee stock plans	361.1		361.1
Income tax benefit from employee stock plans	21.4		21.4
Taxes paid related to net share settlement of equity awards	(11.0)		(1.1)	(9.9)
Share-based compensation expense related to employee stock plans	167.9		167.9
Repurchase and retirement of common stock (in shares)		(0.4)
Repurchase and retirement of common stock	(183.7)		(16.3)	(167.4)
Net income	588.8			588.8
Other comprehensive loss	$ (4.4)				(4.4)
Ending balances (shares) at Dec. 31, 2015	37.4	37.4
Ending balance at Dec. 31, 2015	$ 4,319.5	$ 0.0	3,429.8	899.2	(9.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of options and under stock purchase plan (in shares)		1.5
Issuance of common stock through employee stock plans	580.9		580.9
Income tax benefit from employee stock plans	29.8		29.8
Taxes paid related to net share settlement of equity awards	(24.0)		(2.2)	(21.8)
Share-based compensation expense related to employee stock plans	177.6		177.6
Repurchase and retirement of common stock (in shares)		(0.1)
Repurchase and retirement of common stock	(42.5)		(4.1)	(38.4)
Net income	735.9			735.9
Other comprehensive loss	$ 0.6				0.6
Ending balances (shares) at Dec. 31, 2016	38.8	38.8
Ending balance at Dec. 31, 2016	$ 5,777.8	$ 0.0	$ 4,211.8	$ 1,574.9	$ (8.9)