CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning balance (in shares) at Dec. 31, 2014		128.9	21.1
Beginning balance at Dec. 31, 2014	$ 2,191.4	$ 128.9	$ (1,556.9)	$ 878.4	$ 2,841.9	$ (100.9)
Increase (Decrease) in Stockholders' Equity
Net income	494.9				494.9
Other comprehensive loss, net of tax	(81.7)					(81.7)
Common stock issued under equity plans, including tax benefits (in shares)		2.0
Common stock issued under equity plans, including tax benefits	128.7	$ 2.0		126.7
Stock-based compensation expense	49.9			49.9
Shares issued to acquire business	0.0
Purchases of treasury stock (in shares)			2.6
Purchases of treasury stock	(280.1)		$ (280.1)
Stock issued to effect stock split (in shares)		108.2
Stock issued to effect stock split	0.0	$ 108.2		(108.2)
Retirement of treasury stock			$ 0.0
Ending balance (in shares) at Dec. 31, 2015		239.1	23.7
Ending balance at Dec. 31, 2015	2,503.1	$ 239.1	$ (1,837.0)	946.8	3,336.8	(182.6)
Increase (Decrease) in Stockholders' Equity
Net income	569.5				569.5
Other comprehensive loss, net of tax	(15.8)					(15.8)
Common stock issued under equity plans, including tax benefits (in shares)		3.5
Common stock issued under equity plans, including tax benefits	167.6	$ 3.5		164.1
Stock-based compensation expense	56.9			56.9
Shares issued to acquire business	0.0
Purchases of treasury stock (in shares)			7.3
Purchases of treasury stock	(662.3)		$ (662.3)
Retirement of treasury stock			$ 0.0
Ending balance (in shares) at Dec. 31, 2016		242.6	31.0
Ending balance at Dec. 31, 2016	2,619.0	$ 242.6	$ (2,499.3)	1,167.8	3,906.3	(198.4)
Increase (Decrease) in Stockholders' Equity
Impact to retained earnings from adoption of ASU 2016-09	9.3				9.3
Adjusted beginning balance	2,628.3	$ 242.6	$ (2,499.3)	1,167.8	3,915.6	(198.4)
Net income	583.6				583.6
Other comprehensive loss, net of tax	65.7					65.7
Common stock issued under equity plans, including tax benefits (in shares)		3.0
Common stock issued under equity plans, including tax benefits	113.8	$ 3.0		110.8
Stock-based compensation expense	61.6			61.6
Stock issued to acquire business (in shares)			(2.8)
Shares issued to acquire business	266.5		$ 264.3	2.2
Purchases of treasury stock (in shares)			7.7
Purchases of treasury stock	(763.3)		$ (763.3)
Retirement of treasury stock (in shares)		(33.6)	(33.6)
Retirement of treasury stock	0.0	$ (33.6)	$ 2,746.2	(175.5)	(2,537.1)
Ending balance (in shares) at Dec. 31, 2017		212.0	2.3
Ending balance at Dec. 31, 2017	$ 2,956.2	$ 212.0	$ (252.1)	$ 1,166.9	$ 1,962.1	$ (132.7)