UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 383.6	$ (35.3)	$ 673.6	$ (140.3)
Postretirement plans (net of $0.0 tax provisions in each period)	(13.4)	(11.0)	(40.3)	(33.0)
Foreign currency translation adjustment	0.1	(0.8)	(1.4)	(1.2)
Other comprehensive loss, net of income taxes	(13.3)	(11.8)	(41.7)	(34.2)
Comprehensive income (loss)	370.3	(47.1)	631.9	(174.5)
Less: Net income attributable to noncontrolling interests	8.5	8.9	8.5	12.6
Comprehensive income (loss) attributable to common stockholders	$ 361.8	$ (56.0)	$ 623.4	$ (187.1)