Accumulated Other Comprehensive (Loss) Income Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013		Dec. 31, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cash flow hedges	$ (21.0)	[1]	$ 91.8
Accumulated other comprehensive income [Line Items]
Foreign Currency Translation Adjustment	(54.0)				(70.5)
Reclassification from other comprehensive income to earnings	0
Current period change	16.5		1.1
Net actuarial loss associated with postretirement plans and workers' compensation obligations	(199.4)				(205.8)
Reclassification from other comprehensive income to earnings	6.4	[2]	14.3	[2]
Current period change	0
Prior service cost associated with postretirement plans	(5.0)				12.0
Reclassification from other comprehensive income to earnings	0.4	[2]	(0.1)	[2]
Current period change	(17.4)		0
Cash flow hedges	(33.9)				(155.7)
Net change in fair value	116.2		68.7
Reclassification from other comprehensive income to earnings	5.6	[2]	(77.1)	[2]
Available-for-sale securities	(1.0)				0.8
Net change in fair value	(1.8)		(6.2)
Reclassification from other comprehensive income to earnings	0		0.1
Total accumulated other comprehensive (loss) income	(293.3)				(419.2)
Net change in fair value	114.4
Reclassification from other comprehensive income to earnings	12.4
Current period change	(0.9)
Net actuarial loss postretirement health care and life insurance benefits operating costs and expenses [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net actuarial loss and prior service cost associated with postretirement plans and workers compensation obligations	(3.6)	[2]	(6.0)	[2]
Net actuarial loss defined benefit pension plans operating costs and expenses [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net actuarial loss and prior service cost associated with postretirement plans and workers compensation obligations	(6.2)	[2]	(13.6)	[2]
Net actuarial loss defined benefit pension plans selling and administrative expenses [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net actuarial loss and prior service cost associated with postretirement plans and workers compensation obligations	(1.4)	[2]	(2.8)	[2]
Net actuarial loss insignificant items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net actuarial loss and prior service cost associated with postretirement plans and workers compensation obligations	1.0	[2]	(0.3)	[2]
Net actuarial loss associated with postretirement plans total before income taxes [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net actuarial loss and prior service cost associated with postretirement plans and workers compensation obligations	(10.2)	[2]	(22.7)	[2]
Net actuarial loss associated with postretirement plans and workers compensation obligations income tax benefit [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net actuarial loss and prior service cost associated with postretirement plans and workers compensation obligations	3.8	[2]	8.4	[2]
Prior service cost postretirement plans postretirement health care and life insurance benefits operating costs and expenses [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net actuarial loss and prior service cost associated with postretirement plans and workers compensation obligations	(0.3)	[2]	0.4	[2]
Prior service cost defined benefit pension plans operating costs and expenses [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net actuarial loss and prior service cost associated with postretirement plans and workers compensation obligations	(0.3)	[2]	(0.2)	[2]
Prior service cost associated with postretirement plans total before income taxes [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net actuarial loss and prior service cost associated with postretirement plans and workers compensation obligations	(0.6)	[2]	0.2	[2]
Prior service cost associated with postretirement plans income tax benefit (provision) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Net actuarial loss and prior service cost associated with postretirement plans and workers compensation obligations	0.2	[2]	(0.1)	[2]
Cash flow hedges foreign currency cash flow hedge contracts operating costs and expenses [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cash flow hedges	(18.8)	[2]	85.1	[2]
Cash flow hedges fuel and explosives commodity swaps operating costs and expenses [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cash flow hedges	(2.4)	[2]	6.9	[2]
Cash flow hedges coal trading commodity futures, swaps and options other revenues [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cash flow hedges	17.8	[2]	25.3	[2]
Cash flow hedges insignificant items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cash flow hedges	(0.1)	[2]	(0.1)	[2]
Cash flow hedges total before income taxes [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cash flow hedges	(3.5)	[2]	117.2	[2]
Cash flow hedges income tax provision [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Cash flow hedges	(2.1)	[2]	(40.1)	[2]
Available-for-sale securities debt securities interest income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Available-for-sale securities	$ 0	[2]	$ 0.1	[2],[3]

[1] Includes the reclassification from "Accumulated other comprehensive loss" into earnings of $40.9 million of previously unrecognized gains on foreign currency cash flow hedge contracts monetized in the fourth quarter of 2012.

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

[3] The tax effect associated with the realized gain on sale of debt securities during the three months ended March 31, 2013 was less than $0.1 million.