Emergence from the Chapter 11 Cases and Fresh Start Reporting - Liabilities Subject to Compromise (Details) - USD ($) $ in Millions	Apr. 01, 2017	Dec. 31, 2016
Fresh-Start Adjustment [Line Items]
Debt	$ 8,077.4	$ 8,080.3
Interest payable	172.6	172.6
Environmental liabilities	61.9	61.9
Trade payables	55.2	58.4
Postretirement benefit obligations	23.0	34.6
Other accrued liabilities	26.6	32.4
Liabilities subject to compromise	8,416.7	8,440.2
First Lien, Second Lien And Unsecured Debt
Fresh-Start Adjustment [Line Items]
Debt	7,768.3	7,771.2
Prepetition Letters Of Credit \| Derivative Contract Termination
Fresh-Start Adjustment [Line Items]
Debt	$ 257.3
Prepetition Letters Of Credit \| Secured Debt
Fresh-Start Adjustment [Line Items]
Debt		$ 51.8

Liabilities Subject to Compromise, Accounts Payable

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Liabilities Subject to Compromise, Accrued Interest

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Liabilities Subject to Compromise, Other Accrued Liabilities

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Total amount of liabilities subject to compromise.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 852
-SubTopic 10
-Section 55
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The amount of environmental remediation liabilities included in liabilities subject to compromise.

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Amount classified as pension and other postretirement obligations included in liability subject to compromise.

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