Postretirement Benefits Other Than Pensions - Changes in Fair Value of Plan Assets and Changes in Accumulated Benefit Obligations (Details) - Other Postretirement Benefit Plan, Defined Benefit - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plans’ Assets at Beginning of Year	$ 0.0	$ 0.0
Employer Contributions	1.0	1.0
Plan Participants’ Contributions	0.3	0.3
Benefits Paid	(1.3)	(1.3)
Fair Value of Plan Assets at End of Year	0.0	0.0	$ 0.0
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Accumulated Postretirement Benefit Obligation at Beginning of Year	8.1	11.2
Service Cost	0.1	0.2	0.3
Interest Cost	0.4	0.2	0.1
Plan Participants’ Contributions	0.3	0.3
Benefits Paid	(1.3)	(1.3)
Actuarial Gains	(0.1)	(2.5)
Projected Benefit Obligation at End of Year	7.5	8.1	$ 11.2
Funded Status—Plan Assets in Excess of Projected Benefit Obligation	(7.5)	(8.1)
Unamortized Actuarial Gain Reported in AOCI at End of Year	$ 13.9	$ 16.9