Future Minimum Lease Payments (Details) - Successor $ in Millions	Dec. 31, 2017 USD ($)
Future minimum lease and royalty payments [Line Items]
Capital Leases, 2017	$ 39.9
Capital Leases, 2018	28.1
Capital Leases, 2019	8.1
Capital Leases, 2020	0.5
Capital Leases, 2021	0.5
Capital Leases, 2022 and Thereafter	9.2
Capital Leases, Total minimum lease payments	86.3
Capital Leases, Less interest	10.3
Capital Leases, Present value of minimum capital lease payments	76.0
Operating Leases, 2017	68.5
Operating Leases, 2018	46.7
Operating Leases, 2019	39.3
Operating Leases, 2020	29.0
Operating Leases, 2021	11.2
Operating Leases, 2022 and thereafter	22.9
Operating Leases, Total minimum lease payments	217.6
Coal Lease and Royalty Obligation, 2017	6.9
Coal Lease and Royalty Obligation, 2018	6.7
Coal Lease and Royalty Obligation, 2019	6.5
Coal Lease and Royalty Obligation, 2020	6.3
Coal Lease and Royalty Obligation, 2021	6.1
Coal Lease and Royalty Obligation, 2022 and Thereafter	33.0
Coal Lease and Royalty Obligation, Total minimum lease payments	$ 65.5

Coal Lease And Royalty Obligation Capital Leases Future Minimum Payments Due.

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Coal Lease And Royalty Obligation Capital Leases Future Minimum Payments Due In Five Years

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Coal Lease And Royalty Obligation Capital Leases Future Minimum Payments Due In Four Years.

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Coal Lease And Royalty Obligation Capital Leases Future Minimum Payments Due In Three Years.

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Coal Lease And Royalty Obligation Capital Leases Future Minimum Payments Due In Two Years

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Coal Lease And Royalty Obligation Capital Leases Future Minimum Payments Due Thereafter.

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Coal Lease And Royalty Obligation Future Minimum Payments Due Current.

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Future minimum lease and royalty payments [Line Items]

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Amount of minimum lease payments for capital leases.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84164817&loc=d3e45280-112737

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Amount of minimum lease payments for capital leases due in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of minimum lease payments for capital leases due in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of minimum lease payments for capital leases due in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of minimum lease payments for capital leases due in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of minimum lease payments for capital leases due in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of minimum lease payments for capital leases due after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount necessary to reduce net minimum lease payments to present value for capital leases.

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Present value of minimum lease payments for capital leases net of executory costs, including amounts paid by the lessee to the lessor for insurance, maintenance and taxes.

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Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year.

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Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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