Consolidated Statement of Shareholders' Equity (Unaudited) - USD ($) shares in Millions, $ in Millions	Total	Common Stock	Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss
Beginning balance (in shares) at Dec. 31, 2017		153.1
Beginning balance at Dec. 31, 2017	$ 985.6	$ 1.5	$ 2,911.6	$ (1,831.6)	$ (95.9)
Shareholders' Equity (Deficit) [Roll Forward]
Net income	483.7			483.7
Equity-based compensation expense	26.0		26.0
Stock option exercises (in shares)		0.7
Stock option exercises	24.4		24.4
Coworker Stock Purchase Plan (in shares)		0.1
Coworker stock purchase plan	8.4		8.4
Repurchases of common stock (in shares)		(3.0)
Repurchases of common stock	(232.5)			(232.5)
Dividends paid	(95.5)		0.5	(96.0)
Incentive compensation plan stock withheld for taxes	(27.1)			(27.1)
Foreign currency translation	(17.9)				(17.9)
Unrealized (loss) gain from hedge accounting	3.1				3.1
Realized gain from hedge accounting	2.5				2.5
Ending balance (in shares) at Sep. 30, 2018		150.9
Ending balance at Sep. 30, 2018	1,160.7	$ 1.5	2,970.9	(1,703.5)	(108.2)
Beginning balance (in shares) at Jun. 30, 2018		151.5
Beginning balance at Jun. 30, 2018	1,068.9	$ 1.5	2,953.3	(1,780.8)	(105.1)
Shareholders' Equity (Deficit) [Roll Forward]
Net income	183.7			183.7
Equity-based compensation expense	9.9		9.9
Stock option exercises (in shares)		0.0
Stock option exercises	4.5		4.5
Coworker Stock Purchase Plan (in shares)		0.0
Coworker stock purchase plan	3.0		3.0
Repurchases of common stock (in shares)		(0.6)
Repurchases of common stock	(56.1)			(56.1)
Dividends paid	(31.7)		0.2	(31.9)
Incentive compensation plan stock withheld for taxes	(18.4)			(18.4)
Foreign currency translation	(3.2)				(3.2)
Unrealized (loss) gain from hedge accounting	(1.0)				(1.0)
Realized gain from hedge accounting	1.1				1.1
Ending balance (in shares) at Sep. 30, 2018		150.9
Ending balance at Sep. 30, 2018	1,160.7	$ 1.5	2,970.9	(1,703.5)	(108.2)
Beginning balance (in shares) at Dec. 31, 2018		147.7
Beginning balance at Dec. 31, 2018	975.2	$ 1.5	2,996.9	(1,892.6)	(130.6)
Shareholders' Equity (Deficit) [Roll Forward]
Net income	551.2			551.2
Equity-based compensation expense	36.9		36.9
Stock option exercises (in shares)		1.0
Stock option exercises	27.6		27.6
Coworker stock purchase plan	11.2		11.2
Repurchases of common stock (in shares)		(4.8)
Repurchases of common stock	(493.3)	$ (0.1)		(493.2)
Dividends paid	(128.9)		0.6	(129.5)
Incentive compensation plan stock withheld for taxes	(21.3)			(21.3)
Foreign currency translation	(12.7)				(12.7)
Unrealized (loss) gain from hedge accounting	(12.8)				(12.8)
Realized gain from hedge accounting	2.0				2.0
Ending balance (in shares) at Sep. 30, 2019		143.9
Ending balance at Sep. 30, 2019	935.1	$ 1.4	3,073.2	(1,985.4)	(154.1)
Beginning balance (in shares) at Jun. 30, 2019		145.0
Beginning balance at Jun. 30, 2019	936.1	$ 1.5	3,047.6	(1,973.6)	(139.4)
Shareholders' Equity (Deficit) [Roll Forward]
Net income	201.7			201.7
Equity-based compensation expense	12.9		12.9
Stock option exercises (in shares)		0.3
Stock option exercises	8.6		8.6
Coworker stock purchase plan	3.9		3.9
Repurchases of common stock (in shares)		(1.4)
Repurchases of common stock	(161.1)	$ (0.1)		(161.0)
Dividends paid	(42.6)		0.2	(42.8)
Incentive compensation plan stock withheld for taxes	(9.7)			(9.7)
Foreign currency translation	(14.6)				(14.6)
Unrealized (loss) gain from hedge accounting	(0.4)				(0.4)
Realized gain from hedge accounting	0.3				0.3
Ending balance (in shares) at Sep. 30, 2019		143.9
Ending balance at Sep. 30, 2019	$ 935.1	$ 1.4	$ 3,073.2	$ (1,985.4)	$ (154.1)