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Summary Quarterly Financial Information (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2015 | Sep. 30, 2015 | Jun. 30, 2015 | Mar. 31, 2015 | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014 | Dec. 31, 2016 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments of Debt Restructuring Costs |  |  |  |  | $ 10.3 |  | $ 26.4 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of the unaudited quarterly results of operations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues | $ 1,440.8 |  | $ 1,207.1 |  | 1,040.2 |  | 1,027.2 |  | $ 1,313.1 |  |  |  |  |  |  |  | $ 1,418.9 |  | $ 1,339.3 |  | $ 1,537.9 |  | $ 3,564.7 | $ 4,715.3 | $ 5,609.2 | $ 6,792.2
Operating loss | (44.9) |  | (21.6) |  | (107.7) |  | (102.7) |  | (470.8) |  |  |  |  |  |  |  | (20.4) |  | (975.8) |  | 2.2 |  |  | (276.9) | (1,464.8) | (135.1)
Loss from continuing operations, net of income taxes | (175.2) |  | (97.7) |  | (223.2) |  | (167.7) |  | (502.0) |  |  |  |  |  |  |  | (126.4) |  | (1,006.0) |  | (148.8) |  | (423.6) | (663.8) | (1,783.2) | (695.3)
Net loss | (188.3) |  | (135.8) |  | (226.2) |  | (171.1) |  | (474.3) |  |  |  |  |  |  |  | (283.9) |  | (1,042.3) |  | (157.7) |  | (477.2) | (721.4) | (1,958.2) | (723.5)
Net loss attributable to common stockholders | $ (192.7) |  | $ (137.6) |  | $ (227.9) |  | $ (171.1) |  | $ (473.5) |  |  |  |  |  |  |  | $ (286.7) |  | $ (1,044.1) |  | $ (161.0) |  | (485.1) | $ (729.3) | $ (1,965.3) | $ (733.2)
Basic and diluted EPS — continuing operations(1) | $ (9.82) | [1] | $ (5.44) | [1] | $ (12.30) | [1] | $ (9.17) | [1] | $ (27.50) | [2] |  |  |  |  |  |  | $ (7.09) | [2] | $ (55.53) | [2] | $ (8.44) | [2] |  | $ (36.72) | $ (98.65) | $ (39.51)
Diluted EPS — continuing operations(1) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ (36.72) | $ (98.65) | $ (39.51)
Weighted average shares used in calculating basic and diluted EPS | 18.3 |  | 18.3 |  | 18.3 |  | 18.3 |  | 18.2 |  |  |  |  |  |  |  | 18.2 |  | 18.2 |  | 18.0 |  |  | 18.3 | 18.1 | 17.9
Weighted average shares used in calculating diluted EPS |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 18.3 | 18.1 | 17.9
Summary Quarterly Financial Information (Textuals) [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Asset impairment | $ 230.7 |  |  |  |  |  | $ 17.2 |  | $ 377.0 |  |  |  | $ 900.8 |  |  |  |  |  |  |  |  |  | 230.7 | $ 247.9 | $ 1,277.8 | $ 154.4
Gain (Loss) on Disposition of Assets |  |  |  |  | $ 13.7 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (21.4) | 23.2 | 45.0 | 41.4
Gain (loss) on sale of nonstrategic asset |  |  |  |  | 6.2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income (Loss) from Equity Method Investments | 28.8 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (26.2) | 16.2 | (15.9) | (107.6)
Interest Expense |  |  |  |  |  |  | 126.2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 150.4 | 298.6 | 465.4 | 426.6
Reorganization Items | 33.9 |  | $ 29.7 |  | 95.4 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 159.0 | 159.0 | 0.0 | 0.0
Restructuring and pension settlement charges |  |  |  |  |  |  |  |  |  |  |  |  | 21.2 |  |  |  |  |  |  |  |  |  |  | 15.5 | 23.5 | 26.0
Loss on early debt extinguishment | 29.5 |  |  |  |  |  |  |  |  |  |  |  | (8.3) |  | $ (59.5) |  |  |  |  |  |  |  | 29.5 | (29.5) | (67.8) | (1.6)
Loss from discontinued operations, net of income taxes | 13.1 |  | 38.1 |  |  |  |  |  |  |  | $ 155.1 |  |  |  | 7.6 |  |  |  |  |  |  |  | (53.6) | (57.6) | (175.0) | (28.2)
Additional charge recorded as a result of the damages awarded to Eagle in arbitration |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (15.6) |  |
Remeasurement of foreign taxes |  |  |  |  |  |  |  |  | (0.5) |  | 0.8 |  |  |  | 0.2 |  |  |  |  |  |  |  |  | 2.0 | 22.1 | 21.8
Income Tax Expense (Benefit) |  |  |  |  |  |  |  |  | 7.9 |  |  |  | 67.4 |  |  |  |  |  |  |  |  |  | $ (22.7) | (94.5) | (207.1) | 147.4
Change in fair value of credit support provided to Patriot |  |  |  |  |  |  |  |  |  |  |  |  | 34.7 |  |  |  |  |  |  |  |  |  |  |  |  |
Australia Deferred Tax Assets [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary Quarterly Financial Information (Textuals) [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Valuation Allowance, Deferred Tax Asset, Increase, Amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (82.1) |  |
Australian Mining [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary Quarterly Financial Information (Textuals) [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Asset impairment |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 675.2 | 66.7
US Deferred Tax Assets [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary Quarterly Financial Information (Textuals) [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Valuation Allowance, Deferred Tax Asset, Increase, Amount |  |  |  |  |  |  |  |  | 177.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (2,342.9) |  |
Interest In Middlemount Coal Pty Limited [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary Quarterly Financial Information (Textuals) [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income (Loss) from Equity Method Investments |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 22.6 | (7.0) | (98.5)
Priairie State Campus [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary Quarterly Financial Information (Textuals) [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain (loss) on sale of nonstrategic asset |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6.2 |  |
Nonstrategic Australian mining tenement [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary Quarterly Financial Information (Textuals) [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain (loss) on sale of nonstrategic asset |  |  |  |  | 2.8 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.0 |  |
Scenario, Previously Reported [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Summary of the unaudited quarterly results of operations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Loss from continuing operations, net of income taxes | (186.2) |  | (95.6) |  | (230.8) |  | (161.7) |  | (497.9) |  | (144.4) |  | (1,007.2) |  | (164.4) |  |  |  |  |  |  |  |  | (674.3) | (1,813.9) | (749.1)
Net loss | (199.3) |  | (133.7) |  | (233.8) |  | (165.1) |  | (470.2) |  | (301.9) |  | (1,043.5) |  | (173.3) |  |  |  |  |  |  |  |  | (731.9) | (1,988.9) | (777.3)
Net loss attributable to common stockholders | $ (203.7) |  | $ (135.5) |  | $ (235.5) |  | $ (165.1) |  | $ (469.4) |  | $ (304.7) |  | $ (1,045.3) |  | $ (176.6) |  |  |  |  |  |  |  |  | (739.8) | (1,996.0) | (787.0)
Summary Quarterly Financial Information (Textuals) [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income Tax Expense (Benefit) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ (84.0) | $ (176.4) | $ 201.2
Income (Loss) from Continuing Operations, Per Basic and Diluted Share | $ (10.42) | [3] | $ (5.32) | [3] | $ (12.71) | [3] | $ (8.85) | [3] | $ (27.28) | [4] | $ (8.08) | [4] | $ (55.59) | [4] | $ (9.31) | [4] |  |  |  |  |  |  |  | $ (37.30) | $ (100.34) | $ (42.52)
[1] | EPS for the quarters may not sum to the amounts for the year as each period is computed on a discrete basis.
[2] | EPS for the quarters may not sum to the amounts for the year as each period is computed on a discrete basis
[3] | EPS for the quarters may not sum to the amounts for the year as each period is computed on a discrete basis.
[4] | EPS for the quarters may not sum to the amounts for the year as each period is computed on a discrete basis.

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