UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS’ EQUITY - USD ($) $ in Millions	Total	Common Stock	Additional paid-in capital	Treasury stock	(Accumulated deficit) retained earnings	Accumulated other comprehensive income	Noncontrolling interests
Balance, beginning of period at Dec. 31, 2018		$ 1.4	$ 3,304.7	$ (1,025.1)	$ 1,074.5	$ 40.1	$ 56.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividend equivalent units on dividends declared			7.8
Share-based compensation for equity-classified awards			30.2
Common stock repurchases	$ 300.2			(300.2)
Net (loss) income	91.3				78.5		12.8
Repurchase of employee common stock relinquished for tax withholding	12.3			(12.3)
Dividends declared ($0.000, $0.145, $0.000, and $2.265 per share, respectively)					(251.7)
Postretirement plans and workers' compensation obligations (net of $0.0 tax provisions in each period)	(6.6)					(6.6)
Foreign currency translation adjustment	(1.7)					(1.7)
Distributions to noncontrolling interests							(23.4)
Balance, end of period at Sep. 30, 2019	2,985.0	1.4	3,342.7	(1,337.6)	901.3	31.8	45.4
Balance, beginning of period at Jun. 30, 2019		1.4	3,333.7	(1,193.4)	999.1	35.3	49.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividend equivalent units on dividends declared			0.4
Share-based compensation for equity-classified awards			8.6
Common stock repurchases				(144.2)
Net (loss) income	(78.1)				(82.8)		4.7
Repurchase of employee common stock relinquished for tax withholding				0.0
Dividends declared ($0.000, $0.145, $0.000, and $2.265 per share, respectively)					(15.0)
Postretirement plans and workers' compensation obligations (net of $0.0 tax provisions in each period)	(2.2)					(2.2)
Foreign currency translation adjustment	(1.3)					(1.3)
Distributions to noncontrolling interests							(9.0)
Balance, end of period at Sep. 30, 2019	2,985.0	1.4	3,342.7	(1,337.6)	901.3	31.8	45.4
Balance, beginning of period at Dec. 31, 2019	2,672.5	1.4	3,351.1	(1,367.3)	597.0	31.6	58.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividend equivalent units on dividends declared			0.0
Share-based compensation for equity-classified awards			9.9
Common stock repurchases	0.0			0.0
Net (loss) income	(1,746.2)				(1,741.1)		(5.1)
Repurchase of employee common stock relinquished for tax withholding	1.6			(1.6)
Dividends declared ($0.000, $0.145, $0.000, and $2.265 per share, respectively)					0.0
Postretirement plans and workers' compensation obligations (net of $0.0 tax provisions in each period)	167.9					167.9
Foreign currency translation adjustment	1.8					1.8
Distributions to noncontrolling interests							(3.5)
Balance, end of period at Sep. 30, 2020	1,100.8	1.4	3,361.0	(1,368.9)	(1,144.1)	201.3	50.1
Balance, beginning of period at Jun. 30, 2020		1.4	3,357.2	(1,368.9)	(1,076.9)	26.5	50.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation for equity-classified awards			3.8
Common stock repurchases				0.0
Net (loss) income	(67.1)				(67.2)		0.1
Repurchase of employee common stock relinquished for tax withholding				0.0
Dividends declared ($0.000, $0.145, $0.000, and $2.265 per share, respectively)					0.0
Postretirement plans and workers' compensation obligations (net of $0.0 tax provisions in each period)	172.3					172.3
Foreign currency translation adjustment	2.5					2.5
Balance, end of period at Sep. 30, 2020	$ 1,100.8	$ 1.4	$ 3,361.0	$ (1,368.9)	$ (1,144.1)	$ 201.3	$ 50.1