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Financial Instruments (Details) $ in Millions | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Sep. 30, 2016 USD ($) | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($) | Jul. 26, 2016 USD ($)
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | $ 2,015.5 |  |  |
Financial Instruments and Guarantees with Off-Balance-Sheet Risk (Textuals) [Abstract] |  |  |  |  |  |
Amount in bank guarantees, letters of credit and surety bonds related to road maintenance, performance guarantees and other operations |  |  | 121.0 |  |  |
Amount in Letters of Credit Held as Collateral in Support of Surety Bonds |  |  | 48.0 |  |  |
Amount in letters of credit issued as collateral to support surety bonds |  |  | 72.6 |  |  |
Cash collateral in support of reclamation obligations or activities |  |  | 233.2 |  |  |
Letters of credit in support of reclamation obligations or activities |  | $ 15.7 | 80.0 | $ 126.6 |  |
Total consideration received by Company related to accounts receivable sold under securitization program |  |  | 2,859.9 |  |  |
Cash up front from sale of receivables |  |  | 1,541.7 |  |  |
Additional cash upon collection of underlying receivables |  |  | 1,155.3 |  |  |
Non collected receivables |  |  | 162.9 |  |  |
Reduction in accounts receivable as a result of securitization activity |  |  |  | 168.5 |  |
Expense associated with securitization transactions |  |  | 8.2 | 1.8 | $ 1.5 |
Restricted Cash and Investments, Current |  |  | 54.3 | 0.0 |  |
Maximum Capacity of Securitization Program |  |  | 180.0 | $ 275.0 |  |
Restricted Cash and Cash Equivalents |  |  | 40.5 |  |  |
Restricted Cash and Investments, Noncurrent |  |  | 71.4 |  |  |
DTA and PBGC [Member] |  |  |  |  |  |
Financial Instruments and Guarantees with Off-Balance-Sheet Risk (Textuals) [Abstract] |  |  |  |  |  |
Letters of credit outstanding |  |  | $ 37.0 |  |  |
Dominion Terminal Associates Partnership [Member] |  |  |  |  |  |
Financial Instruments and Guarantees with Off-Balance-Sheet Risk (Textuals) [Abstract] |  |  |  |  |  |
Ownership percentage of equity method investment |  |  | 37.50% |  |  |
DTA Lease Term |  |  | 30 |  |  |
Repayments of Lines of Credit |  | 39.9 |  |  |  |
Line of Credit Assumed |  | $ 42.7 |  |  |  |
Pension Plans Agreement With PBG and TXU Europe [Member] |  |  |  |  |  |
Financial Instruments and Guarantees with Off-Balance-Sheet Risk (Textuals) [Abstract] |  |  |  |  |  |
Defined benefit pension plans requiring special contributions |  |  | 2 |  |  |
Letter of credit maintained by the Company in favor of the PBGC |  |  | $ 37.0 |  |  |
Guarantee in place from TXU Europe Limited |  |  | 110.0 |  |  |
Reclamation Obligations [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 1,701.7 |  |  |
Coal Lease Obligations [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 94.0 |  |  |
Workers' Compensation Obligations [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 61.8 |  |  |
Other [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk | [1] |  | 158.0 |  |  |
Financial Standby Letter of Credit [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 381.5 |  |  |
Self bonding [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 1,094.2 |  |  |
Self bonding [Member] | Reclamation Obligations [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 1,094.2 |  |  |
Self bonding [Member] | Coal Lease Obligations [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 0.0 |  |  |
Self bonding [Member] | Workers' Compensation Obligations [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 0.0 |  |  |
Self bonding [Member] | Other [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk | [1] |  | 0.0 |  |  |
Self bonding [Member] | Financial Standby Letter of Credit [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 0.0 |  |  |
Surety Bond [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 448.2 |  |  |
Surety Bond [Member] | Reclamation Obligations [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 319.6 |  |  |
Surety Bond [Member] | Coal Lease Obligations [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 94.0 |  |  |
Surety Bond [Member] | Workers' Compensation Obligations [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 19.1 |  |  |
Surety Bond [Member] | Other [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk | [1] |  | 15.5 |  |  |
Surety Bond [Member] | Financial Standby Letter of Credit [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk | [2] |  | 64.5 |  |  |
Bank Guarantees [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 79.2 |  |  |
Bank Guarantees [Member] | Reclamation Obligations [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 54.7 |  |  |
Bank Guarantees [Member] | Coal Lease Obligations [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 0.0 |  |  |
Bank Guarantees [Member] | Workers' Compensation Obligations [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 0.0 |  |  |
Bank Guarantees [Member] | Other [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk | [1] |  | 24.5 |  |  |
Bank Guarantees [Member] | Financial Standby Letter of Credit [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 83.8 |  |  |
Letters of credit [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 393.9 |  |  |
Letters of credit [Member] | Reclamation Obligations [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 233.2 |  |  |
Letters of credit [Member] | Coal Lease Obligations [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 0.0 |  |  |
Letters of credit [Member] | Workers' Compensation Obligations [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 42.7 |  |  |
Letters of credit [Member] | Other [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk | [1] |  | 118.0 |  |  |
Letters of credit [Member] | Financial Standby Letter of Credit [Member] |  |  |  |  |  |
Guarantee Obligations [Line Items] |  |  |  |  |  |
Financial instruments with off balance sheet risk |  |  | 233.2 |  |  |
Parent Company [Member] |  |  |  |  |  |
Financial Instruments and Guarantees with Off-Balance-Sheet Risk (Textuals) [Abstract] |  |  |  |  |  |
Restricted Cash and Investments, Current |  |  | 13.8 |  |  |
Wyoming [Member] | Self bonding [Member] | Reclamation Obligations [Member] |  |  |  |  |  |
Financial Instruments and Guarantees with Off-Balance-Sheet Risk (Textuals) [Abstract] |  |  |  |  |  |
Letters of credit in support of reclamation obligations or activities |  |  |  |  |  | $ 0.8
Indiana [Member] | Self bonding [Member] | Reclamation Obligations [Member] |  |  |  |  |  |
Financial Instruments and Guarantees with Off-Balance-Sheet Risk (Textuals) [Abstract] |  |  |  |  |  |
Letters of credit in support of reclamation obligations or activities |  |  |  |  |  | 7.5
Illinois [Member] | Self bonding [Member] | Reclamation Obligations [Member] |  |  |  |  |  |
Financial Instruments and Guarantees with Off-Balance-Sheet Risk (Textuals) [Abstract] |  |  |  |  |  |
Letters of credit in support of reclamation obligations or activities |  |  |  |  |  | $ 3.2
U.S Mining [Member] |  |  |  |  |  |
Financial Instruments and Guarantees with Off-Balance-Sheet Risk (Textuals) [Abstract] |  |  |  |  |  |
Surety Bonds Outstanding For Reclamation |  |  | 1,413.8 |  |  |
Costs Incurred, Asset Retirement Obligation Incurred |  |  | 471.1 |  |  |
Australian Mining [Member] |  |  |  |  |  |
Financial Instruments and Guarantees with Off-Balance-Sheet Risk (Textuals) [Abstract] |  |  |  |  |  |
Costs Incurred, Asset Retirement Obligation Incurred |  |  | 287.7 |  |  |
Cash collateral in support of reclamation obligations or activities |  |  | $ 233.2 |  |  |
[1] | Other includes the $37.0 million in letters of credit related to the PBGC, as described below, and an additional $121.0 million in bank guarantees, letters of credit and surety bonds related to road maintenance, performance guarantees and other operations.
[2] | A total of $72.6 million of letters of credit issued as collateral to support surety bonds related to Patriot have been excluded from above as they no longer represent off-balance sheet obligations as discussed in Note 27. "Matters Related to the Bankruptcy of Patriot Coal Corporation".

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