Reorganization Items, Net 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
Reorganizations [Abstract]
Liabilities subject to compromise	$ 8,416.7	$ 8,416.7
Successor Common Stock (at par)	(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
Write-off of Predecessor debt issuance costs	(18.1)
Gain on settlement of claims	$ 3,031.2	$ (3,031.2)	$ (12.8)