UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Statement of Comprehensive Income [Abstract]
Net income	$ 202.8	$ 410.6	$ 485.6	$ 290.0
Postretirement plans (net of $0.0 tax provisions in each period)	(13.4)	(13.5)	(26.8)	(26.9)
Foreign currency translation adjustment	(0.4)	(3.4)	(0.6)	(1.5)
Other comprehensive loss, net of income taxes	(13.8)	(16.9)	(27.4)	(28.4)
Comprehensive income	189.0	393.7	458.2	261.6
Less: Net income attributable to noncontrolling interests	23.6	1.1	37.9	0.0
Comprehensive income attributable to common stockholders	$ 165.4	$ 392.6	$ 420.3	$ 261.6