Shareowners' Equity (Deficit) - Schedule of Changes in Accumulated Other Comprehensive Loss by Component (Details) - USD ($) $ in Millions		1 Months Ended		2 Months Ended	3 Months Ended	8 Months Ended	9 Months Ended
		Sep. 30, 2021	Sep. 30, 2021	Sep. 07, 2021	Sep. 30, 2020	Sep. 07, 2021	Sep. 30, 2020
Changes in Accumulated Other Comprehensive Loss by Component [Roll Forward]
Beginning balance		$ 0.0	$ (122.2)	$ (139.2)	$ (189.6)	$ (159.7)	$ (170.1)
Remeasurement of benefit obligations			0.0	0.0	3.2	6.0	(11.5)
Reclassifications, net				19.0	5.0	30.4	15.1
Unrealized loss on cash flow hedges arising during the period, net			0.0	(0.6)	(0.5)	(0.1)	(11.3)
Foreign currency gain (loss)		(1.2)	(1.2)	(1.4)	2.0	1.2	(2.1)
Ending balance		(1.2)	(1.2)	(122.2)	(179.9)	(122.2)	(179.9)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Changes in Accumulated Other Comprehensive Loss by Component [Roll Forward]
Beginning balance		0.0	(122.1)	(124.9)	(159.4)	(138.8)	(152.0)
Remeasurement of benefit obligations					3.2	6.0	(11.5)
Reclassifications, net	[1]			2.8	3.2	10.7	10.5
Unrealized loss on cash flow hedges arising during the period, net				0.0	0.0	0.0	0.0
Foreign currency gain (loss)		0.0		0.0	0.0	0.0	0.0
Ending balance		0.0	0.0	(122.1)	(153.0)	(122.1)	(153.0)
Accumulated Gain (Loss), Cash Flow Hedge, Including Noncontrolling Interest
Changes in Accumulated Other Comprehensive Loss by Component [Roll Forward]
Beginning balance		0.0	(0.1)	(15.7)	(22.7)	(19.7)	(14.7)
Remeasurement of benefit obligations					0.0	0.0	0.0
Reclassifications, net	[2]			16.2	1.8	19.7	4.6
Unrealized loss on cash flow hedges arising during the period, net	[3]			(0.6)	(0.5)	(0.1)	(11.3)
Foreign currency gain (loss)		0.0		0.0	0.0	0.0	0.0
Ending balance		0.0	0.0	(0.1)	(21.4)	(0.1)	(21.4)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Changes in Accumulated Other Comprehensive Loss by Component [Roll Forward]
Beginning balance		0.0	0.0	1.4	(7.5)	(1.2)	(3.4)
Remeasurement of benefit obligations					0.0	0.0	0.0
Reclassifications, net				0.0	0.0	0.0	0.0
Unrealized loss on cash flow hedges arising during the period, net				0.0	0.0	0.0	0.0
Foreign currency gain (loss)		(1.2)		(1.4)	2.0	1.2	(2.1)
Ending balance		$ (1.2)	$ (1.2)	$ 0.0	$ (5.5)	$ 0.0	$ (5.5)

[1] These reclassifications are included in the other components of net periodic pension and postretirement benefit plans expense and represent amortization of prior service benefit and actuarial loss, net of tax and pension settlement charges, net of tax. The other components of net periodic pension and postretirement benefit plans expense are recorded in "Other components of pension and postretirement benefit plans expense" on the Condensed Consolidated Statements of Operations. See Note 9 for further disclosures.

[2] These reclassifications are reported within "Interest expense" and "Other (income) expense, net" on the Condensed Consolidated Statements of Operations when the hedged transactions impact earnings.

[3] The unrealized loss, net on cash flow hedges represents the change in the fair value of the derivative instruments that occurred during the period, net of tax. The unrealized loss on cash flow hedges is recorded in "Other current liabilities" and "Other noncurrent liabilities" on the Condensed Consolidated Balance Sheets in the Predecessor period. See Note 8 for further disclosures.