Pension and Postretirement Plans - Schedule of Pension and Postretirement Benefit Costs (Details) - USD ($) $ in Millions	4 Months Ended	8 Months Ended	12 Months Ended
	Dec. 31, 2021	Sep. 07, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Interest cost on projected benefit obligation	4.7	10.2	18.8	23.9
Expected return on plan assets	(10.2)	(19.9)	(29.0)	(30.7)
Amortization of:
Prior service benefit	0.0	0.0	0.0	0.0
Actuarial loss	0.0	16.0	18.1	13.7
Pension settlement charges	0.0	0.0	3.8	0.0
Pension/postretirement (benefit) cost	(5.5)	6.3	11.7	6.9
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	0.1	0.3	0.4	0.6
Interest cost on projected benefit obligation	0.8	1.8	3.7	5.0
Expected return on plan assets	0.0	0.0	0.0	0.0
Amortization of:
Prior service benefit	0.0	(1.7)	(2.5)	(2.5)
Actuarial loss	0.0	0.0	1.2	1.8
Pension settlement charges	0.0	0.0	0.0	0.0
Pension/postretirement (benefit) cost	$ 0.9	$ 0.4	$ 2.8	$ 4.9