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Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract] |  |  |  |  |  |  |  |  |
Other Comprehensive Income, Available-For-Sale Securities, Net Unamortized (Gain) Loss Arising During Period, Net of Tax | $ 0.0 | $ 0.0 |  | $ 0.0 |  |  |  |  |
After-tax components of comprehensive income (loss) |  |  |  |  |  |  |  |  |
Foreign Currency Translation Adjustment, Beginning Balance | (146.4) | (111.5) |  | (70.5) |  |  |  |  |
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax | 0.0 | 0.0 |  | 0.0 |  |  |  |  |
Reclassification from other comprehensive income to earnings | 0.0 | 0.0 |  | 0.0 |  |  |  |  |
Foreign currency translation adjustment | (1.8) | (34.9) |  | (41.0) |  |  |  |  |
Foreign Currency Translation Adjustment, Ending Balance | (148.2) | (146.4) |  | (111.5) |  |  |  |  |
Accumulated Other Comprehensive Income Loss Acturial Loss Associated With Postretirement Plans And Workers Compensation Obligation Net Of Tax |  |  |  |  |  | $ (256.3) | $ (263.8) | $ (317.5) | $ (205.8)
Other Comprehensive Income (Loss), Postretirement Plans and Workers' Compensation Obligations, Period Increase Decrease, Net of Tax | 0.0 | 0.0 |  | 0.0 |  |  |  |  |
Reclassification from other comprehensive income to earnings | 21.0 | 35.6 |  | 31.0 |  |  |  |  |
Current period change | (13.5) | 18.1 |  | (142.7) |  |  |  |  |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax | 4.5 | (10.4) |  | (11.4) |  |  |  |  |
Prior Service Cost Associated with Postretirement Plans, Beginning Balance | 31.8 | 25.1 |  | 12.0 |  |  |  |  |
Other Comprehensive Income (Loss), Prior Service Cost Associated with Postretirement Plans, Period Increase Decrease, Net of Tax | 0.0 | 0.0 |  | 0.0 |  |  |  |  |
Reclassification from other comprehensive income to earnings | (5.6) | (3.7) |  | 1.7 |  |  |  |  |
Prior Service Cost Associated with Postretirement Plans, Ending Balance | 21.7 | 31.8 |  | 25.1 |  |  |  |  |
Cash Flow Hedges, Beginning Balance | (240.5) | (360.9) |  | (155.7) |  |  |  |  |
Increase in fair value of cash flow hedges, net of tax | 0.0 | (131.3) |  | (195.0) |  |  |  |  |
Reclassification for realized losses (gains) included in net loss | 146.3 | 251.7 |  | (10.2) |  |  |  |  |
Current Period Change | 0.0 | 0.0 |  | 0.0 |  |  |  |  |
Cash Flow Hedges, Ending Balance | (94.2) | (240.5) |  | (360.9) |  |  |  |  |
Available-For-Sale Securities Adjustment, Beginning Balance | 0.0 | 0.0 |  | 0.8 |  |  |  |  |
Unrealized holding losses on available-for-sale securities | 0.0 | 0.0 |  | (3.7) |  |  |  |  |
Reclassification from other comprehensive income to earnings | 0.0 | 0.0 |  | (2.9) |  |  |  |  |
Available-For-Sale Securities Adjustment, Ending Balance | 0.0 | 0.0 |  | 0.0 |  |  |  |  |
Total Accumulated Other Comprehensive Income (Loss), Beginning Balance | (477.0) | (618.9) |  | (764.8) |  | $ (477.0) | $ (618.9) | $ (764.8) | $ (419.2)
Accumulated Other Comprehensive Loss Net Change in Fair Value of Cash Flow Hedges and Available for Sale Securities | 0.0 | (131.3) |  | (198.7) |  |  |  |  |
Total Accumulated Other Comprehensive Income (Loss), Reclassification | 161.7 | 283.6 |  | 25.4 |  |  |  |  |
Other Comprehensive Income Loss Current Period Change Net Of Tax | (19.8) | (6.4) |  | (172.3) |  |  |  |  |
Total Accumulated Other Comprehensive Income (Loss), Ending Balance | (477.0) | (618.9) |  | (764.8) |  |  |  |  |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax [Abstract] |  |  |  |  |  |  |  |  |
Cash flow hedges |  | (438.4) | [1] | $ (47.9) | [2] |  |  |  |
Definedbenefitpensionplanspriorservicecost [Member] |  |  |  |  |  |  |  |  |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax [Abstract] |  |  |  |  |  |  |  |  |
Net actuarial loss and prior service cost associated with postretirement plans and workers compensation obligations | 0.3 | 1.0 |  |  |  |  |  |  |
IncomeTaxProvisionCashFlowHedges [Member] |  |  |  |  |  |  |  |  |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax [Abstract] |  |  |  |  |  |  |  |  |
Cash flow hedges | 85.9 | 134.0 |  |  |  |  |  |  |
TotalBeforeIncomeTaxesCashFlowHedges [Member] |  |  |  |  |  |  |  |  |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax [Abstract] |  |  |  |  |  |  |  |  |
Cash flow hedges | 232.2 | 385.7 |  |  |  |  |  |  |
InsignificantItemsCashFlowHedges [Member] |  |  |  |  |  |  |  |  |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax [Abstract] |  |  |  |  |  |  |  |  |
Cash flow hedges | 0.5 | 0.7 |  |  |  |  |  |  |
CoalTradingOtherRevenues [Member] |  |  |  |  |  |  |  |  |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax [Abstract] |  |  |  |  |  |  |  |  |
Cash flow hedges | 0.0 | (51.8) |  |  |  |  |  |  |
CommoditySwapsOperatingCostsAndExpenses [Member] |  |  |  |  |  |  |  |  |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax [Abstract] |  |  |  |  |  |  |  |  |
Cash flow hedges | 86.1 | 120.4 |  |  |  |  |  |  |
ForeignCurrencyCashFlowHedgeContractsOperatingCostsAndExpenses [Member] |  |  |  |  |  |  |  |  |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax [Abstract] |  |  |  |  |  |  |  |  |
Cash flow hedges | 145.6 | 316.4 |  |  |  |  |  |  |
Incometaxprovisionpriorservicecost [Member] |  |  |  |  |  |  |  |  |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax [Abstract] |  |  |  |  |  |  |  |  |
Net actuarial loss and prior service cost associated with postretirement plans and workers compensation obligations | (3.3) | (2.1) |  |  |  |  |  |  |
PriorServiceCostAssociatedWithPostretirementPlansAndWorkersCompensationObligationsTotalBeforeIncomeTaxes [Member] |  |  |  |  |  |  |  |  |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax [Abstract] |  |  |  |  |  |  |  |  |
Net actuarial loss and prior service cost associated with postretirement plans and workers compensation obligations | (8.9) | (5.8) |  |  |  |  |  |  |
PostretirementHealthCareAndLifeInsuranceBenefitsOperatingCostsAndExpensesPriorServiceCost [Member] |  |  |  |  |  |  |  |  |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax [Abstract] |  |  |  |  |  |  |  |  |
Net actuarial loss and prior service cost associated with postretirement plans and workers compensation obligations | (9.2) | (6.8) |  |  |  |  |  |  |
IncomeTaxProvisionActuarialLoss [Member] |  |  |  |  |  |  |  |  |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax [Abstract] |  |  |  |  |  |  |  |  |
Net actuarial loss and prior service cost associated with postretirement plans and workers compensation obligations | (12.4) | (20.9) |  |  |  |  |  |  |
NetActuarialLossAssociatedWithPostretirementPlansAndWorkersCompensationObligationsTotalBeforeIncomeTaxes [Member] |  |  |  |  |  |  |  |  |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax [Abstract] |  |  |  |  |  |  |  |  |
Net actuarial loss and prior service cost associated with postretirement plans and workers compensation obligations | 33.4 | 56.5 |  |  |  |  |  |  |
InsignificantItemsActuarialLoss [Member] |  |  |  |  |  |  |  |  |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax [Abstract] |  |  |  |  |  |  |  |  |
Net actuarial loss and prior service cost associated with postretirement plans and workers compensation obligations | (11.7) | (8.0) |  |  |  |  |  |  |
DefinedBenefitPensionPlansSellingAndAdministrativeExpensesActuarialLoss [Member] |  |  |  |  |  |  |  |  |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax [Abstract] |  |  |  |  |  |  |  |  |
Net actuarial loss and prior service cost associated with postretirement plans and workers compensation obligations | 4.2 | 6.7 |  |  |  |  |  |  |
DefinedBenefitPensionPlansOperatingCostsAndExpensesActuarialLoss [Member] |  |  |  |  |  |  |  |  |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax [Abstract] |  |  |  |  |  |  |  |  |
Net actuarial loss and prior service cost associated with postretirement plans and workers compensation obligations | 20.5 | 32.9 |  |  |  |  |  |  |
PostretirementHealthCareAndLifeInsuranceBenefitsOperatingCostsAndExpensesActuarialLoss [Member] |  |  |  |  |  |  |  |  |
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax [Abstract] |  |  |  |  |  |  |  |  |
Net actuarial loss and prior service cost associated with postretirement plans and workers compensation obligations | $ 20.4 | $ 24.9 |  |  |  |  |  |  |
[1] | (1) Includes the reclassification from "Accumulated other comprehensive loss" into earnings of $14.9 million of previously unrecognized gains on foreign currency cash flow hedge contracts monetized in the fourth quarter of 2012.
[2] | Includes the reclassification from "Accumulated other comprehensive loss" into earnings of $136.9 million of previously unrecognized gains on foreign currency cash flow hedge contracts monetized in the fourth quarter of 2012.

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