Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Accumulated other comprehensive income [Line Items]
Foreign Currency Translation Adjustment		$ (144.0)		$ (144.0)		$ (146.4)
Foreign Currency Translation Adjustment, Reclassification from other comprehensive income to earnings				0.0
Foreign Currency Translation Adjustment, Current period change		1.5	$ (15.3)	2.4	$ (41.5)
Net Actuarial Loss Associated With Postretirement Plans And Workers' Compensation Obligation		(248.0)		(248.0)		(263.8)
Net actuarial loss associated with postretirement plans and workers' compensation obligations, Reclassification from other comprehensive income to earnings	[1]	5.3	12.5	15.8	30.3
Net actuarial loss associated with postretirement plans and workers' compensation obligations, Current period change				0.0
Prior Service Cost Associated with Postretirement Plans		26.8		26.8		31.8
Prior service cost associated with postretirement plans, Reclassification from other comprehensive income to earnings	[1]	(1.7)	(1.7)	(5.0)	(3.5)
Prior service cost associated with postretirement plans, Current period change				0.0
Cash Flow Hedges		(121.5)		(121.5)		(240.5)
Cash flow hedges, Net change in fair value		0.0	(115.6)	0.0	(100.4)
Cash flow hedges, Reclassification from other comprehensive income to earnings	[1]	29.9	68.9	119.0	183.9
Cash flow hedges, Current period change				0.0
Total Accumulated Other Comprehensive Loss		(486.7)		(486.7)		$ (618.9)
Total Accumulated Other Comprehensive Loss, Reclassification from other comprehensive income to earnings				129.8
Total Accumulated Other Comprehensive Loss, Current period change				2.4
PostretirementHealthCareAndLifeInsuranceBenefitsOperatingCostsAndExpensesActuarialLoss [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), before Tax	[1]	(5.2)	(6.3)	(15.4)	(18.7)
DefinedBenefitPensionPlansOperatingCostsAndExpensesActuarialLoss [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), before Tax	[1]	(5.1)	(8.2)	(15.3)	(24.7)
DefinedBenefitPensionPlansSellingAndAdministrativeExpensesActuarialLoss [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), before Tax	[1]	(1.1)	(1.6)	(3.2)	(5.0)
InsignificantItemsActuarialLoss [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), before Tax	[1]	3.0	2.0	8.8	6.0
NetActuarialLossAssociatedWithPostretirementPlansAndWorkersCompensationObligationsTotalBeforeIncomeTaxes [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), before Tax	[1]	(8.4)	(14.1)	(25.1)	(42.4)
IncomeTaxProvisionActuarialLoss [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), Tax	[1]	3.1	1.6	9.3	12.1
PostretirementHealthCareAndLifeInsuranceBenefitsOperatingCostsAndExpensesPriorServiceCost [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive (Income) Loss, Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit), before Tax	[1]	2.8	1.7	8.3	5.1
Definedbenefitpensionplanspriorservicecost [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive (Income) Loss, Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit), before Tax	[1]	(0.1)	(0.2)	(0.3)	(0.7)
PriorServiceCostAssociatedWithPostretirementPlansAndWorkersCompensationObligationsTotalBeforeIncomeTaxes [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive (Income) Loss, Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit), before Tax	[1]	2.7	1.5	8.0	4.4
Incometaxprovisionpriorservicecost [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive (Income) Loss, Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit), Tax	[1]	(1.0)	0.2	(3.0)	(0.9)
ForeignCurrencyCashFlowHedgeContractsOperatingCostsAndExpenses [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	[1]	(28.0)	(84.5)	(122.1)	(238.9)
CommoditySwapsOperatingCostsAndExpenses [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	[1]	(19.4)	(32.4)	(66.4)	(87.7)
CoalTradingOtherRevenues [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	[1]	0.0	13.2	0.0	35.6
InsignificantItemsCashFlowHedges [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	[1]	(0.1)	(0.2)	(0.4)	(0.5)
TotalBeforeIncomeTaxesCashFlowHedges [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, before Tax	[1]	(47.5)	(103.9)	(188.9)	(291.5)
IncomeTaxProvisionCashFlowHedges [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax	[1]	$ 17.6	$ 35.0	$ 69.9	$ 107.6

[1] Presented as gains (losses) in the unaudited condensed consolidated statements of operations.