Pension and Postretirement Plans - Amounts Recognized in Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2021	Sep. 07, 2021	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Pension and postretirement benefit obligations (noncurrent liability)	$ 141.1		$ 200.2
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Total		$ 101.6
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Accrued payroll and benefits (current liability)	2.0		2.1
Pension and postretirement benefit obligations (noncurrent liability)	50.7		101.4
Total	52.7		103.5
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Prior service (cost) benefit, net of tax of ($0.1), $3.4	0.0		(0.1)
Actuarial gain (loss), net of tax of $0.7, ($39.0), $0.1, ($4.3)	2.0		(136.1)
Total	2.0		(136.2)
Prior service costs, tax			(0.1)
Actuarial gain (loss), tax	0.7		(39.0)
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Accrued payroll and benefits (current liability)	7.8		8.5
Pension and postretirement benefit obligations (noncurrent liability)	89.8		98.0
Total	97.6		106.5
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Prior service (cost) benefit, net of tax of ($0.1), $3.4	0.0		13.7
Actuarial gain (loss), net of tax of $0.7, ($39.0), $0.1, ($4.3)	0.6		(16.3)
Total	0.6		(2.6)
Prior service costs, tax			3.4
Actuarial gain (loss), tax	$ 0.1		$ (4.3)