Reorganization Items, Net (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended	12 Months Ended
	Apr. 01, 2017	Mar. 31, 2018	Apr. 01, 2017	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018
Fresh-Start Adjustment [Line Items]
Fresh-Start Adjustment, Reorganization Gain (Loss), Net	$ 3,031.2		$ (3,031.2)			$ (12.8)
Fresh-Start Adjustment, Increase (Decrease), Stockholders' Equity, before Tax			(3,363.1)			0.0
Fresh-Start Income Tax Adjustments, Increase (Decrease) in Expense			(253.9)			0.0
Legal and Advisory Professional Fees	$ 336.4		42.5			0.0
Gain on Settlement of Other Claims, Net			0.7			0.0
Reorganization Items, net		$ 12.8	$ 627.2	$ 0.0	$ 0.0	$ (12.8)