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, 2022	Dec. 31, 2020
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period				$ 562.5
Fair value of plan assets at end of period		$ 562.5		393.8
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period		633.3	$ 674.1	611.9
Service cost		0.0	0.0	0.0	$ 0.0
Interest cost		4.7	10.2	16.3	18.8
Hawaii Plan Adjustment		0.0	0.0	0.0
Plan Amendment		0.0	0.0	0.0
Actuarial (gain) loss	[1],[2]	11.4	17.0	146.3
Benefits paid		(12.8)	(26.6)	(34.9)
Settlements	[3]	(1.9)	(7.4)	(7.5)
Other		0.0	0.0	0.0
Benefit obligation at end of period		611.9	633.3	439.5	674.1
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	559.2
Actual (loss) return on plan assets		1.3	32.5	(128.3)
Employer contributions		0.8	2.7	2.1
Benefits paid		(12.8)	(26.6)	(34.9)
Settlements	[3]	(1.9)	(7.4)	(7.5)
Fair value of plan assets at end of period		559.2	571.8	390.6	570.6
Unfunded status		(52.7)	(61.5)	48.9
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	100.9
Service cost		0.1	0.3	0.8	0.4
Interest cost		0.8	1.8	4.2	3.7
Hawaii Plan Adjustment		0.0	0.0	45.9
Plan Amendment		0.0	0.0	(4.7)
Actuarial (gain) loss	[1],[2]	0.6	4.0	37.1
Benefits paid		(2.4)	(5.4)	(9.8)
Settlements	[3]	0.0	0.0	0.0
Other		0.2	0.5	2.2
Benefit obligation at end of period		100.9	102.8	102.4	109.6
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	3.3
Actual (loss) return on plan assets		0.0	0.1	0.1
Employer contributions		2.4	5.1	7.3
Benefits paid		(2.4)	(5.0)	(7.5)
Settlements	[3]	0.0	0.0	0.0
Fair value of plan assets at end of period		3.3	3.3	3.2	$ 3.1
Unfunded status		$ (97.6)	$ (99.5)	$ 99.2

[1] The actuarial (gain) recorded during the year ended December 31, 2022 and in the Successor and Predecessor periods in 2021 for the pension plans was primarily driven by an increase in the discount rate in each of the respective periods.

[2] The actuarial (gain) recorded for the year ended December 31, 2022 for the postretirement plans was primarily driven by an increase in the discount rate, updated census data and the result of actual versus expected benefit payments. The actuarial (gain) recorded in the Successor and Predecessor periods in 2021 for the postretirement plans was primarily due to an increase in the discount rate and the result of actual versus expected benefit payments.

[3] Participant elections to take lump sum payments that exceeded the settlement accounting threshold and have been categorized as settlements.