UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ (67.1)	$ (78.1)	$ (1,746.2)	$ 91.3
Postretirement plans and workers' compensation obligations (net of $0.0 tax provisions in each period)	172.3	(2.2)	167.9	(6.6)
Foreign currency translation adjustment	2.5	(1.3)	1.8	(1.7)
Other comprehensive income (loss), net of income taxes	174.8	(3.5)	169.7	(8.3)
Comprehensive income (loss)	107.7	(81.6)	(1,576.5)	83.0
Less: Net income (loss) attributable to noncontrolling interests	0.1	4.7	(5.1)	12.8
Comprehensive income (loss) attributable to common stockholders	$ 107.6	$ (86.3)	$ (1,571.4)	$ 70.2