Emergence from the Chapter 11 Cases and Fresh Start Reporting - Reorganization Items, Net (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
	Apr. 01, 2017	Apr. 01, 2017	Jun. 30, 2016	Jun. 30, 2016
Fresh-Start Adjustment [Line Items]
Gain on settlement of claims (per above)	$ (3,031.2)
Professional fees	336.4
Income Tax Effect Related to Predecessor Deferred Tax Liabilities
Fresh-Start Adjustment [Line Items]
Fresh start income tax adjustments, net	(177.8)
Income Tax Effect Related to AOCI
Fresh-Start Adjustment [Line Items]
Fresh start income tax adjustments, net	(81.5)
Income Tax Effect Related to Unrecognized Tax Benefits
Fresh-Start Adjustment [Line Items]
Fresh start income tax adjustments, net	(6.7)
Income Tax Effect Related to Predecessor Deferred Tax Assets of Discontinued Operations
Fresh-Start Adjustment [Line Items]
Fresh start income tax adjustments, net	12.1
Predecessor
Fresh-Start Adjustment [Line Items]
Gain on settlement of claims (per above)	(3,031.2)	$ (3,031.2)	$ 0.0	$ 0.0
Fresh start adjustments, net (per above)	3,363.1	3,363.1	0.0	0.0
Fresh start income tax adjustments, net	(253.9)	(253.9)	0.0	0.0
Loss on termination of derivative contracts	0.0	0.0	75.2	75.2
Professional fees	0.0	42.5	21.6	21.6
Accounts payable settlement gains	0.0	(0.7)	(0.2)	(0.2)
Interest income	0.0	(0.4)	(0.2)	(0.2)
Other	0.0	0.0	(1.0)	(1.0)
Reorganization items, net	585.8	627.2	95.4	95.4
Cash paid for Reorganization items, net	$ 14.4	$ 45.8	$ 0.0	$ 0.0