Other Postretirement Benefit Plans (Details) - Postretirement Plan - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Net periodic benefit credit:
Service cost	$ 0.0	$ 0.1	$ 0.0	$ 0.1
Interest cost	0.5	0.3	1.0	0.7
Amortization of prior service credit	(2.1)	(2.5)	(4.2)	(5.0)
Net periodic benefit cost (credit)	$ (1.6)	$ (2.1)	$ (3.2)	$ (4.2)