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Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Apr. 01, 2017 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Advance royalty recoupment reserve [Member] |  |  |  |  |  |  |  |  |
Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |  |  |  |  |  |  |
Charges to Other Accounts |  | $ (7.4) | [1] |  | $ 0.0 |  | $ 0.0 |  |
Reserve for materials and supplies [Member] |  |  |  |  |  |  |  |  |
Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |  |  |  |  |  |  |
Charges to Other Accounts |  | (6.1) | [1] |  | 0.0 |  | 0.0 |  |
Allowance for Doubtful Accounts [Member] |  |  |  |  |  |  |  |  |
Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |  |  |  |  |  |  |
Charges to Other Accounts |  | (12.8) | [1] |  | 0.0 |  | 0.0 |  |
Valuation Allowance of Deferred Tax Assets [Member] |  |  |  |  |  |  |  |  |
Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |  |  |  |  |  |  |
Charges to Other Accounts |  | 28.1 | [1] |  | 0.0 |  | 0.0 |  |
Predecessor | Advance royalty recoupment reserve [Member] |  |  |  |  |  |  |  |  |
Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |  |  |  |  |  |  |
Charges to Cost and Expense |  | 0.0 |  |  | 0.5 |  | 0.0 |  |
Deductions |  | (0.4) | [2] |  | (1.0) | [3] | (0.9) | [3] |
Other |  | 0.0 |  |  | 0.0 |  | 1.6 | [4] |
Valuation Allowances and Reserves, Balance |  | 0.0 |  |  | 7.8 |  | 8.3 |  | $ 7.6
Predecessor | Reserve for materials and supplies [Member] |  |  |  |  |  |  |  |  |
Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |  |  |  |  |  |  |
Charges to Cost and Expense |  | 0.5 |  |  | 4.3 |  | 0.4 |  |
Deductions | [2] | 0.0 |  |  | (3.4) |  | (0.3) |  |
Other |  | 0.0 |  |  | 0.0 |  | 0.0 |  |
Valuation Allowances and Reserves, Balance |  | 0.0 |  |  | 5.6 |  | 4.7 |  | 4.6
Predecessor | Allowance for Doubtful Accounts [Member] |  |  |  |  |  |  |  |  |
Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |  |  |  |  |  |  |
Charges to Cost and Expense |  | 0.0 |  |  | 7.9 |  | 8.0 |  |
Deductions | [2] | (0.3) |  |  | (1.4) |  | (7.2) |  |
Other |  | 0.0 |  |  | 0.0 |  | 0.0 |  |
Valuation Allowances and Reserves, Balance |  | 0.0 |  |  | 13.1 |  | 6.6 |  | 5.8
Predecessor | Valuation Allowance of Deferred Tax Assets [Member] |  |  |  |  |  |  |  |  |
Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |  |  |  |  |  |  |
Charges to Cost and Expense |  | (777.2) |  |  | 2,453.9 |  | 452.9 |  |
Deductions | [2] | 0.0 |  |  | 0.0 |  | 0.0 |  |
Other |  | 0.0 |  |  | (30.5) | [5] | (205.3) | [5] |
Valuation Allowances and Reserves, Balance |  | 3,288.4 |  |  | $ 4,037.5 |  | $ 1,614.1 |  | $ 1,366.5
Successor | Advance royalty recoupment reserve [Member] |  |  |  |  |  |  |  |  |
Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |  |  |  |  |  |  |
Charges to Cost and Expense |  |  |  | $ 0.0 |  |  |  |  |
Charges to Other Accounts |  |  |  | 0.0 |  |  |  |  |
Deductions | [2] |  |  | 0.0 |  |  |  |  |
Other |  |  |  | 0.0 |  |  |  |  |
Valuation Allowances and Reserves, Balance |  | 0.0 |  | 0.0 |  |  |  |  |
Successor | Reserve for materials and supplies [Member] |  |  |  |  |  |  |  |  |
Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |  |  |  |  |  |  |
Charges to Cost and Expense |  |  |  | 1.0 |  |  |  |  |
Charges to Other Accounts |  |  |  | 0.0 |  |  |  |  |
Deductions | [2] |  |  | (0.4) |  |  |  |  |
Other |  |  |  | 0.0 |  |  |  |  |
Valuation Allowances and Reserves, Balance |  | 0.0 |  | 0.6 |  |  |  |  |
Successor | Allowance for Doubtful Accounts [Member] |  |  |  |  |  |  |  |  |
Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |  |  |  |  |  |  |
Charges to Cost and Expense |  |  |  | 4.6 |  |  |  |  |
Charges to Other Accounts |  |  |  | 0.0 |  |  |  |  |
Deductions | [2] |  |  | 0.0 |  |  |  |  |
Other |  |  |  | 0.0 |  |  |  |  |
Valuation Allowances and Reserves, Balance |  | 0.0 |  | 4.6 |  |  |  |  |
Successor | Valuation Allowance of Deferred Tax Assets [Member] |  |  |  |  |  |  |  |  |
Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |  |  |  |  |  |  |
Charges to Cost and Expense |  |  |  | (744.9) |  |  |  |  |
Charges to Other Accounts |  |  |  | 0.0 |  |  |  |  |
Deductions | [2] |  |  | 0.0 |  |  |  |  |
Other | [6] |  |  | (111.0) |  |  |  |  |
Valuation Allowances and Reserves, Balance |  | $ 3,288.4 |  | $ 2,432.5 |  |  |  |  |
[1] | Fresh start reporting adjustments.
[2] | Reserves utilized, unless otherwise indicated.
[3] | Deductions to advance royalty recoupment reserve represents the termination of federal and state leases.
[4] | Balances transferred from other accounts.
[5] | Includes the impact of the decrease in Australian dollar exchange rates.
[6] | Release of valuation allowance primarily related to carrybacks of U.S. net operating losses.

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- Definition Amount of increase (decrease) in the allowances and reserves, which consist of the valuation and qualifying accounts that are either netted against the cost of an asset or that reflect a liability established to represent expected future costs, from adjustments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-09) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690 + Details
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- Definition Total of allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-09) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690 + Details
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- Definition Amount of increase in the allowances and reserves, which consist of the valuation and qualifying accounts that are either netted against the cost of an asset or that reflect a liability established to represent expected future costs, from charges to costs and expenses. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-09) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690 + Details
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- Definition Amount of increase in the allowances and reserves, which consist of the valuation and qualifying accounts that are either netted against the cost of an asset or that reflect a liability established to represent expected future costs, from charges to accounts other than costs and expenses. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-09) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690 + Details
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