Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 42.6	$ 31.7	$ 105.7	$ 102.3
Other comprehensive income:
Amortization of net actuarial losses and prior service costs, net of income taxes of $3.8 million, $3.3 million, $11.4 million, and $10.0 million	11.5	10.1	34.5	30.3
Comprehensive income	$ 54.1	$ 41.8	$ 140.2	$ 132.6