Pension and Postretirement Plans - Benefit Obligation and Funded Status (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
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period			$ 573.7
Fair value of plan assets at end of period		$ 562.5		$ 573.7
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period		633.3	674.1	652.9
Service cost		0.0	0.0	0.0	$ 0.0
Interest cost		4.7	10.2	18.8	23.9
Actuarial (gain) loss	[1],[2]	(11.4)	(17.0)	62.8
Benefits paid		(12.8)	(26.6)	(39.3)
Retiree drug subsidy received		0.0	0.0	0.0
Settlements	[3]	(1.9)	(7.4)	(21.1)
Other		0.0	0.0	0.0
Benefit obligation at end of period		611.9	633.3	674.1	652.9
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period		571.8	570.6	538.8
Actual return on plan assets		1.3	32.5	84.5
Employer contributions		0.8	2.7	7.7
Retiree drug subsidy received		0.0	0.0	0.0
Benefits paid		(12.8)	(26.6)	(39.3)
Settlements	[3]	(1.9)	(7.4)	(21.1)
Fair value of plan assets at end of period		559.2	571.8	570.6	538.8
Unfunded status		(52.7)	(61.5)	(103.5)
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period		102.8	109.6	116.3
Service cost		0.1	0.3	0.4	0.6
Interest cost		0.8	1.8	3.7	5.0
Actuarial (gain) loss	[1],[2]	(0.6)	(4.0)	(3.5)
Benefits paid		(2.4)	(5.4)	(7.9)
Retiree drug subsidy received		0.0	0.2	0.1
Settlements	[3]	0.0	0.0	0.0
Other		0.2	0.3	0.5
Benefit obligation at end of period		100.9	102.8	109.6	116.3
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period		3.3	3.1	4.3
Actual return on plan assets		0.0	0.1	0.1
Employer contributions		2.4	5.1	6.5
Retiree drug subsidy received		0.0	0.3	0.1
Benefits paid		(2.4)	(5.3)	(7.9)
Settlements	[3]	0.0	0.0	0.0
Fair value of plan assets at end of period		3.3	3.3	3.1	$ 4.3
Unfunded status		$ (97.6)	$ (99.5)	$ (106.5)

[1] The actuarial (gain) recorded in the Successor and Predecessor periods in 2021 for the postretirement plans is primarily due to an increase in the discount rate and the result of actual versus expected benefit payments. The actuarial (gain) recorded for the period ending December 31, 2020 is primarily due to updated participant assumptions for the Hawaii plans partially offset by changes to the discount rate for both plans.

[2] The actuarial (gain) recorded in the Successor and Predecessor periods in 2021 for the pension plans was primarily driven by an increase in the discount rate. The actuarial loss recorded during the period ended December 31, 2020 for the pension plans was primarily driven by changes in the discount rate as well as gains or losses to record pension assets to fair value.

[3] The decrease in pension plan settlements in the Successor and Predecessor periods in 2021 compared to 2020 is due to participant elections in 2020 to take lump sum payments upon termination as result of the voluntary severance program offered to employees in both Cincinnati and Hawaii. The extent of the funding exceeded the settlement accounting threshold, and as such in all periods presented, these activities have been categorized as settlements.