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	$ 13.7	$ 42.5	$ 57.9	$ 105.6
Other comprehensive income:
Amortization of net actuarial losses and prior service costs, net of income taxes of $1.8 million, $3.8 million, $5.3 million, and $11.4 million	5.2	11.5	15.6	34.5
Comprehensive income	$ 18.9	$ 54.0	$ 73.5	$ 140.1