Unaudited Condensed Consolidated Statement of Changes in Stockholders' Equity - USD ($) $ in Millions	Total	Preferred Stock	Common Stock	Additional Paid-in Capital	Treasury Stock	Retained earnings	Total Accumulated Other Comprehensive Income	Noncontrolling Interest
Balance, beginning of period at Dec. 31, 2017		$ 576.0	$ 1.0	$ 2,590.3	$ (175.9)	$ 613.6	$ 1.4	$ 49.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Impact of adoption of Accounting Standards Update 2014-09						(22.5)
Net income	$ 220.3					322.8
Dividend equivalent units on dividends declared				0.8		(30.1)
Series A Convertible Preferred Stock conversions		(576.0)	0.4	678.1		(102.5)
Share-based compensation for equity-classified awards				16.5
Common stock repurchases	374.5				(374.5)
Repurchase of employee common stock relinquished for tax withholding	14.5				(14.5)
Net income	323.4							0.6
Distributions to noncontrolling interests								(6.6)
Postretirement plans and workers' compensation obligations (net of $0.0 tax provisions in each period)							0.0
Foreign currency translation adjustment	(3.0)						(3.0)
Balance, end of period at Jun. 30, 2018	3,545.3	0.0	1.4	3,285.7	(564.9)	781.3	(1.6)	43.4
Balance, beginning of period at Mar. 31, 2018		0.0	1.4	3,276.9	(351.4)	682.3	0.6	40.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Impact of adoption of Accounting Standards Update 2014-09						0.0
Net income	113.7					113.7
Dividend equivalent units on dividends declared				0.4		(14.7)
Series A Convertible Preferred Stock conversions		0.0	0.0	0.0		0.0
Share-based compensation for equity-classified awards				8.4
Common stock repurchases					(199.0)
Repurchase of employee common stock relinquished for tax withholding					(14.5)
Net income	116.4							2.7
Distributions to noncontrolling interests								0.0
Postretirement plans and workers' compensation obligations (net of $0.0 tax provisions in each period)							0.0
Foreign currency translation adjustment	(2.2)						(2.2)
Balance, end of period at Jun. 30, 2018	3,545.3	0.0	1.4	3,285.7	(564.9)	781.3	(1.6)	43.4
Balance, beginning of period at Dec. 31, 2018	3,451.6	0.0	1.4	3,304.7	(1,025.1)	1,074.5	40.1	56.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Impact of adoption of Accounting Standards Update 2014-09						0.0
Net income	161.3					161.3
Dividend equivalent units on dividends declared				7.4		(236.7)
Series A Convertible Preferred Stock conversions		0.0	0.0	0.0		0.0
Share-based compensation for equity-classified awards				21.6
Common stock repurchases	156.0				(156.0)
Repurchase of employee common stock relinquished for tax withholding	12.3				(12.3)
Net income	169.4							8.1
Distributions to noncontrolling interests								(14.4)
Postretirement plans and workers' compensation obligations (net of $0.0 tax provisions in each period)							(4.4)
Foreign currency translation adjustment	(0.4)						(0.4)
Balance, end of period at Jun. 30, 2019	3,225.8	0.0	1.4	3,333.7	(1,193.4)	999.1	35.3	49.7
Balance, beginning of period at Mar. 31, 2019		0.0	1.4	3,322.3	(1,125.3)	978.3	38.0	47.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Impact of adoption of Accounting Standards Update 2014-09						0.0
Net income	37.1					37.1
Dividend equivalent units on dividends declared				1.4		(16.3)
Series A Convertible Preferred Stock conversions		0.0	0.0	0.0		0.0
Share-based compensation for equity-classified awards				10.0
Common stock repurchases					(57.2)
Repurchase of employee common stock relinquished for tax withholding					(10.9)
Net income	39.5							2.4
Distributions to noncontrolling interests								(0.1)
Postretirement plans and workers' compensation obligations (net of $0.0 tax provisions in each period)							(2.2)
Foreign currency translation adjustment	(0.5)						(0.5)
Balance, end of period at Jun. 30, 2019	$ 3,225.8	$ 0.0	$ 1.4	$ 3,333.7	$ (1,193.4)	$ 999.1	$ 35.3	$ 49.7