Postretirement Benefit Plans (Details) - Postretirement Plan - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Jan. 31, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Interest cost		$ 0.4	$ 0.6	$ 1.1	$ 1.6
Expected return on plan assets		0.0	(0.1)	0.0	(0.3)
Amortization of prior service credit		(2.6)	(2.4)	(7.6)	(7.3)
Net periodic benefit credit		(2.2)	(1.9)	(6.4)	(5.9)
Net periodic benefit cost	$ 11.1
Service cost		$ 0.0	$ 0.0	$ 0.1	$ 0.1