Gain on Settlement of Liabilities Subject to Compromise (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
	Apr. 01, 2017	Apr. 01, 2017	Dec. 31, 2018
Fresh-Start Adjustment [Line Items]
Liabilities subject to compromise	$ 8,416.7	$ 8,416.7
Less amounts issued to settle claims:
Successor Common Stock	0.7	0.7
Successor Series A Convertible Preferred Stock	1,305.4	1,305.4
Successor Additional paid-in capital	(1,774.9)	(1,774.9)
Issuance of Successor Notes	(1,000.0)	(1,000.0)
Issuance of Successor Term Loan	(950.0)	(950.0)
Cash payments and accruals for claims and professional fees	(336.4)	(42.5)	$ 0.0
Other:
Write-off of Predecessor debt issuance costs, see also (e) below	(18.1)
Total pre-tax gain on plan effects, see also (j) below	$ (3,031.2)	$ 3,031.2	$ 12.8