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Summary of Significant Accounting Policies Discussion (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions | 9 Months Ended | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Dec. 31, 2016 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014 | Sep. 30, 2016 | Apr. 12, 2016 | Mar. 31, 2016 | Dec. 31, 2013
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Other current assets | $ 486.6 | $ 486.6 | $ 447.6 |  |  |  |  |
First Lien Exit Facility |  | 1.95 |  |  |  |  |  |
Other Assets, Noncurrent | 910.4 | $ 910.4 | 363.7 |  |  |  |  |
Total assets | 11,777.7 | 11,777.7 | 10,946.9 | $ 13,191.1 |  |  |  |
Long-term Debt and Capital Lease Obligations, Current | 20.2 | 20.2 | 5,874.9 |  |  |  |  |
Long-term Debt and Capital Lease Obligations | 0.0 | 0.0 | 366.3 |  |  |  |  |
Liabilities | $ 11,439.9 | $ 11,439.9 | $ 10,028.4 |  |  |  |  |
Initial Offering Period |  | 750 |  |  |  |  |  |
Proceeds from Issuance of Private Placement |  | $ 750.0 |  |  |  |  |  |
Equity Investment necessary to consummate Reorg Plan |  | 1.5 |  |  |  |  |  |
Take-back Paper |  | 1.5 |  |  |  |  |  |
Summary Of Significant Accounting Policies Discussion Textuals [Abstract] |  |  |  |  |  |  |  |
Stockholders' Equity, Reverse Stock Split |  | Pursuant to the authorization provided at a special meeting of the Company's stockholders held on September 16, 2015, the Company completed a 1-for-15 reverse stock split of the shares of the Company’s common stock on September 30, 2015 (the Reverse Stock Split). Refer to Note 1. "Summary of Significant Accounting Policies" for additional details surrounding the Reverse Stock Split. | Pursuant to the authorization provided at a special meeting of the Company's stockholders held on September 16, 2015, the Company completed a 1-for-15 reverse stock split of the shares of the Company’s common stock on September 30, 2015 (the Reverse Stock Split). As a result of the Reverse Stock Split, every 15 shares of issued and outstanding common stock were combined into one issued and outstanding share of Common Stock, without any change in the par value per share. |  |  |  |  |
Common Stock, Shares Authorized | 53.3 | 53.3 |  |  |  |  |  |
Common Stock, Par or Stated Value Per Share | $ 0.01 | $ 0.01 |  |  |  |  |  |
Cash and cash equivalents | $ 872.3 | $ 872.3 | $ 261.3 | 298.0 |  | $ 652.1 |  | $ 444.0
Period considered to treat short-term, highly liquid investments as cash equivalents |  | three months or less |  |  |  |  |  |
Other-than-temporary impairment losses on marketable securities |  | $ 0.0 | 4.7 | 4.7 |  |  |  |
Other-than-temporary impairment losses on equity and cost method investments |  | $ 276.5 | 0.0 |  |  |  |  |
Recognition of tax benefits from uncertain tax positions |  | greater than fifty percent likelihood of being realized upon ultimate settlement |  |  |  |  |  |
Restructuring charges for voluntary and involuntary workforce reductions | $ 2.8 | $ 15.5 | 23.5 | 26.0 |  |  |  |
Asset impairment charges related to long-lived assets |  | 247.9 | 1,001.3 | 149.7 |  |  |  |
Foreign currency remeasurement (loss) gains |  | 7.4 | (6.4) | (1.3) |  |  |  |
Foreign currency translation adjustment |  | $ 1.8 | $ 34.9 | $ 41.0 |  |  |  |
Buildings and improvements [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Estimated useful life |  | 3 to 34 |  |  |  |  |  |
Machinery and equipment [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Estimated useful life |  | 3 to 34 |  |  |  |  |  |
Leasehold improvements [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Estimated useful life |  | Shorter of Useful Life or Remaining Life of Lease |  |  |  |  |  |
Interest In Middlemount Coal Pty Limited [Member] |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies Discussion Textuals [Abstract] |  |  |  |  |  |  |  |
Ownership percentage of equity method investment | 50.00% | 50.00% |  |  |  |  |  |
Minimum [Member] | Buildings and improvements [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Estimated useful life |  | 1 |  |  |  |  |  |
Minimum [Member] | Machinery and equipment [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Estimated useful life |  | 1 |  |  |  |  |  |
Maximum [Member] | Buildings and improvements [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Estimated useful life |  | 37 |  |  |  |  |  |
Maximum [Member] | Machinery and equipment [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Estimated useful life |  | 37 |  |  |  |  |  |
Common Stock [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, Reverse Stock Splits |  | 278.0 |  |  |  |  |  |
Common Stock, Shares, issues post reverse stock split | 19.0 | 19.0 |  |  |  |  |  |
Stock Authorized During Period, Shares, Reverse Stock Splits |  |  | 800.0 |  |  |  |  |
Summary Of Significant Accounting Policies Discussion Textuals [Abstract] |  |  |  |  |  |  |  |
Common Stock, Shares Authorized | 53.3 | 53.3 | 53.3 |  |  |  |  |
Common Stock, Par or Stated Value Per Share | $ 0.01 | $ 0.01 | $ 0.01 |  |  |  |  |
Debt burden reduced at exit of bankruptcy [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Long-term Debt | $ 6,600.0 | $ 6,600.0 |  |  |  |  |  |
Revolving Credit Facility [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Long-term Debt | 1,558.1 | 1,558.1 | $ 0.0 |  |  |  | $ 947.0 |
Summary Of Significant Accounting Policies Discussion Textuals [Abstract] |  |  |  |  |  |  |  |
Exit facility, maximum borrowing capacity | 1,650.0 | 1,650.0 |  |  |  |  |  |
6.50% Senior Notes due September 2020 [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Long-term Debt | $ 645.8 | $ 645.8 | 645.5 |  |  |  |  |
Summary Of Significant Accounting Policies Discussion Textuals [Abstract] |  |  |  |  |  |  |  |
Stated interest rate - percentage | 6.50% | 6.50% |  |  | 6.50% |  |  |
10.00% Senior Secured Second Lien Notes Due 2022 [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Long-term Debt | $ 962.3 | $ 962.3 | 960.4 |  |  |  |  |
Face amount of senior notes | $ 1,000.0 | $ 1,000.0 |  |  |  |  |  |
Summary Of Significant Accounting Policies Discussion Textuals [Abstract] |  |  |  |  |  |  |  |
Stated interest rate - percentage | 10.00% | 10.00% |  |  |  |  |  |
6.00% Senior Notes due November 2018 [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Long-term Debt | $ 1,509.9 | $ 1,509.9 | 1,508.9 |  |  |  |  |
Summary Of Significant Accounting Policies Discussion Textuals [Abstract] |  |  |  |  |  |  |  |
Stated interest rate - percentage | 6.00% | 6.00% |  |  |  |  |  |
6.25% Senior Notes due November 2021 [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Long-term Debt | $ 1,327.7 | $ 1,327.7 | 1,327.0 |  |  |  |  |
Summary Of Significant Accounting Policies Discussion Textuals [Abstract] |  |  |  |  |  |  |  |
Stated interest rate - percentage | 6.25% | 6.25% |  |  | 6.25% |  |  |
7.875% Senior Notes [Member] |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies Discussion Textuals [Abstract] |  |  |  |  |  |  |  |
Stated interest rate - percentage | 7.875% | 7.875% |  |  |  |  |  |
Term Loan Facility [Member] |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies Discussion Textuals [Abstract] |  |  |  |  |  |  |  |
Stated interest rate - percentage | 4.50% | 4.50% |  |  |  |  |  |
Exit facility, maximum borrowing capacity | $ 950.0 | $ 950.0 |  |  |  |  |  |
6.000% Senior Secured Notes Due 2022 [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Face amount of senior notes | $ 500.0 | $ 500.0 |  |  |  |  |  |
Summary Of Significant Accounting Policies Discussion Textuals [Abstract] |  |  |  |  |  |  |  |
Stated interest rate - percentage | 6.00% | 6.00% |  |  |  |  |  |
6.375% Senior Secured Notes Due 2022 [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Face amount of senior notes | $ 500.0 | $ 500.0 |  |  |  |  |  |
Summary Of Significant Accounting Policies Discussion Textuals [Abstract] |  |  |  |  |  |  |  |
Stated interest rate - percentage | 6.375% | 6.375% |  |  |  |  |  |
Paid to second lien noteholders in partial satisfaction of their claims [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Cash | $ 450.0 | $ 450.0 |  |  |  |  |  |
Second Lien Notes |  | 450 |  |  |  |  |  |
First Lien Debtholders [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
First Lien Debt |  | 450 |  |  |  |  |  |
Class 5B Claims [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Pro Rate Share in Cash | 75.0 | $ 75.0 |  |  |  |  |  |
Class 5A Claims [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Cash | 5.0 | $ 5.0 |  |  |  |  |  |
Eurocurrency Rate [Member] | Term Loan Facility [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum |  | 1.00% |  |  |  |  |  |
Non-Debtor Subsidiaries [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Other current assets | 416.2 | $ 416.2 |  |  |  |  |  |
Lease Commitments |  | 189 |  |  |  |  |  |
Other Assets, Noncurrent | 596.7 | $ 596.7 |  |  |  |  |  |
Total assets | 6,012.9 | 6,012.9 |  |  |  |  |  |
Long-term Debt and Capital Lease Obligations, Current | 0.9 | 0.9 |  |  |  |  |  |
Liabilities | 2,042.7 | 2,042.7 |  |  |  |  |  |
Summary Of Significant Accounting Policies Discussion Textuals [Abstract] |  |  |  |  |  |  |  |
Cash and cash equivalents | 477.8 | 477.8 |  |  |  | $ 543.6 |  |
Restructuring charges for voluntary and involuntary workforce reductions | 0.6 |  |  |  |  |  |  |
Other Current Assets [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Deferred Finance Costs, Current | (55.5) | (55.5) |  |  |  |  |  |
Other Noncurrent Assets [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Deferred Finance Costs, Current | (18.9) | (18.9) |  |  |  |  |  |
Assets [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Deferred Finance Costs, Current | (74.4) | (74.4) |  |  |  |  |  |
Long-term Debt and Capital Lease Obligations, Current [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Deferred Finance Costs, Current | (55.5) | (55.5) |  |  |  |  |  |
Long-term Debt and Capital Lease Obligations [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Deferred Finance Costs, Current | (18.9) | (18.9) |  |  |  |  |  |
Liability [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Deferred Finance Costs, Current | $ (74.4) | $ (74.4) |  |  |  |  |  |
Peabody Energy [Member] |  |  |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |  |
Other current assets |  |  | 503.1 |  |  |  |  |
Other Assets, Noncurrent |  |  | 382.6 |  |  |  |  |
Total assets |  |  | 11,021.3 |  |  |  |  |
Long-term Debt and Capital Lease Obligations, Current |  |  | 5,930.4 |  |  |  |  |
Long-term Debt and Capital Lease Obligations |  |  | 385.2 |  |  |  |  |
Liabilities |  |  | $ 10,102.8 |  |  |  |  |

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