Postretirement Benefit Plans (Details) - Postretirement Plan - USD ($) $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Jan. 31, 2021	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Interest cost		$ 0.3	$ 0.5	$ 0.7	$ 1.0
Expected return on plan assets		0.0	(0.1)	0.0	(0.2)
Amortization of prior service credit		(2.5)	(2.5)	(5.0)	(4.9)
Net periodic benefit credit		(2.1)	(2.0)	(4.2)	(4.0)
Net periodic benefit cost	$ 11.1
Service cost		$ 0.1	$ 0.1	$ 0.1	$ 0.1