Intangible Contract Assets and Liabilities - Balances and Balance Sheet Classifications (Details) - Successor - Fresh Start Reporting - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Fresh-Start Adjustment [Line Items]
Assets	$ 88.5	$ 177.2
Liabilities	96.0	133.4
Net Total	(7.5)	(43.8)
Take-or-pay contracts
Fresh-Start Adjustment [Line Items]
Assets	0.0	0.0
Coal supply agreements
Fresh-Start Adjustment [Line Items]
Assets	88.5	177.2
Net Total	(56.1)	(134.5)
Take-or-pay contracts
Fresh-Start Adjustment [Line Items]
Liabilities	63.6	90.7
Coal supply agreements
Fresh-Start Adjustment [Line Items]
Liabilities	(32.4)	(42.7)
Investments and other assets
Fresh-Start Adjustment [Line Items]
Assets	88.5	177.2
Liabilities	0.0	0.0
Net Total	(88.5)	(177.2)
Accounts payable and accrued expenses
Fresh-Start Adjustment [Line Items]
Assets	0.0	0.0
Liabilities	19.5	27.6
Other noncurrent liabilities
Fresh-Start Adjustment [Line Items]
Assets	0.0	0.0
Liabilities	$ 76.5	$ 105.8

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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

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