Postretirement Benefit Plans - Amount Recognized in Accumulated Other Comprehensive Income Loss (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ 9.9	$ 9.1
Prior service cost (benefit)	(18.2)	(24.3)
Total	(8.3)	(15.2)
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	9.5	5.7
Prior service cost (benefit)	0.3	0.3
Total	9.8	6.0
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	0.4	3.4
Prior service cost (benefit)	(18.5)	(24.6)
Total	$ (18.1)	$ (21.2)