Pension and Postretirement Plans - Amounts Recognized in AOCI (Details) - USD ($) $ in Millions	4 Months Ended	8 Months Ended	12 Months Ended
	Dec. 31, 2021	Sep. 07, 2021	Dec. 31, 2022
Pension Plans, Defined Benefit [Member]
Prior service cost recognized:
Reclassification adjustments	$ 0.0	$ 0.0	$ 0.0
Actuarial gain (loss) recognized:
Reclassification adjustments	0.0	15.6	0.0
Actuarial (loss) gain arising during the period	2.7	29.5	(9.4)
Other Postretirement Benefit Plans, Defined Benefit [Member]
Prior service cost recognized:
Reclassification adjustments	0.0	(1.7)	4.7
Actuarial gain (loss) recognized:
Reclassification adjustments	0.0	0.0	(0.8)
Actuarial (loss) gain arising during the period	$ 0.7	$ 4.0	$ 37.6