Intangible Contract Assets and Liabilities - Balances and Balance Sheet Classifications (Details) - Successor - Fresh Start Reporting $ in Millions	Sep. 30, 2017 USD ($)
Fresh-Start Adjustment [Line Items]
Assets	$ 231.6
Liabilities	(155.3)
Net Total	76.3
Take-Or-Pay Contracts
Fresh-Start Adjustment [Line Items]
Assets	0.0
Coal supply agreements
Fresh-Start Adjustment [Line Items]
Assets	231.6
Net Total	184.7
Take-Or-Pay Contracts
Fresh-Start Adjustment [Line Items]
Liabilities	(108.4)
Coal supply agreements
Fresh-Start Adjustment [Line Items]
Liabilities	46.9
Investments and other assets
Fresh-Start Adjustment [Line Items]
Assets	231.6
Liabilities	0.0
Net Total	231.6
Accounts payable and accrued expenses
Fresh-Start Adjustment [Line Items]
Assets	0.0
Liabilities	(35.7)
Other noncurrent liabilities
Fresh-Start Adjustment [Line Items]
Assets	0.0
Liabilities	$ (119.6)

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- Definition

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

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+ References

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+ References

No definition available.

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