Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 39.2	$ 44.1	$ 70.6	$ 82.8
Other comprehensive income:
Amortization of net actuarial losses and prior service credits, net of income taxes of $3.4 million, $2.4 million, $6.7 million, and $4.6 million	10.0	7.0	20.2	14.0
Comprehensive income	$ 49.2	$ 51.1	$ 90.8	$ 96.8