Retirement Benefits - Narrative (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended							12 Months Ended				12 Months Ended						12 Months Ended			12 Months Ended					12 Months Ended
	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 US Plans [Member]	Dec. 31, 2011 US Plans [Member]	Dec. 31, 2013 US Plans [Member]	Dec. 31, 2010 US Plans [Member]	Dec. 31, 2012 Non-US Plans [Member]	Dec. 31, 2011 Non-US Plans [Member]	Dec. 31, 2013 Non-US Plans [Member]	Dec. 31, 2010 Non-US Plans [Member]	Dec. 31, 2012 UMWA Plans Postretirement Medical [Member]	Dec. 31, 2011 UMWA Plans Postretirement Medical [Member]	Dec. 31, 2010 UMWA Plans Postretirement Medical [Member]	Dec. 31, 2012 Black Lung And Other Plans Postretirement [Member]	Dec. 31, 2011 Black Lung And Other Plans Postretirement [Member]	Dec. 31, 2010 Black Lung And Other Plans Postretirement [Member]	Dec. 31, 2012 Pension plan [Member]	Dec. 31, 2011 Pension plan [Member]	Dec. 31, 2009 Pension plan [Member]	Dec. 31, 2012 Retirement benefits other than pension [Member]	Dec. 31, 2011 Retirement benefits other than pension [Member]	Dec. 31, 2010 Retirement benefits other than pension [Member]	Dec. 31, 2012 Primary U.S. retirement plan [Member]	Dec. 31, 2013 Nonqualified U.S. pension plan [Member]	Dec. 31, 2012 Us Definded Contribtution Expense [Member]	Dec. 31, 2011 Us Definded Contribtution Expense [Member]	Dec. 31, 2010 Us Definded Contribtution Expense [Member]	Dec. 31, 2012 Other Defined Contribution Plans Expense [Member]	Dec. 31, 2011 Other Defined Contribution Plans Expense [Member]	Dec. 31, 2010 Other Defined Contribution Plans Expense [Member]	Dec. 31, 2012 UMWA Excise Tax [Member]	Dec. 31, 2011 UMWA Excise Tax [Member]
Amounts in AOCI to be recognized in retirement cost in next fiscal year [Abstract]
Net Gains Losses to be recognized in retirement cost next fiscal year																			$ 51.6			$ 20.5
Net Prior Service Cost Credit to be recognized in retirement cost next fiscal year																			2.3			1.7
Accumulated benefit obligation					1,031.3	990.7			345.1	278.8
Estimated contributions							12.9				22.5															0.9
UMWA obligation increase due to "Cadillac" plan excise tax		(47.0)	(253.6)	(67.8)	(23.1)	(133.1)			(32.4)	(20.0)			(6.3)	97.6		(2.2)	2.9		(55.5)	(153.1)		(8.5)	100.5										31.0	21.3
Retirement Benefit Plan Remeasurements [Abstract]
Common stock value per share for stock contribution																									$ 24.90
Aggregate value of shares contributed to pension plan		9.0
Remeasurement discount rate		4.20%	4.60%	5.30%					5.30%	5.40%		5.80%	3.90%	4.40%	5.30%	3.50%	4.20%	4.80%				3.90%	4.40%	5.20%
2010 Healthcare reform black lung obligation increase		9.8	0	19.3	0	0			(11.7)	0			0	0		1.9	0		(11.7)	0		1.9	0
Black lung obligation					1,031.3	990.7		890.1	392.3	306.9		289.6	525.3	529.6	474.3	53.0	60.9	62.2	1,423.6	1,297.6	1,179.7	578.3	590.5	536.5
Black lung health care cost trend rate													7.00%	7.00%		5.00%
Black lung health care cost ultimate rate													5.00%	5.00%
UMWA Medical Plans with Prescription Drug Benefits [Abstract]
Estimated reduction in per capita claim costs for participants over 65 years old													9.00%
Effect of Subsidy on Net Periodic Postretirement Benefit Cost													5.0	4.5	4.5
Reduction in Accumulated Postretirement Benefit Obligation for Subsidy													62.4	60.2
Other Benefit Plans [Abstract]
Multiemployer Pension Expense		0.3	0	2.3
Matching defined contribution expense		$ 7.1	$ 20.8	$ 20.3																							$ 4.6	$ 16.9	$ 16.3	$ 2.5	$ 3.9	$ 4.0
Defined contribution plan employer matching contribution percent	100.00%	100.00%	125.00%
Defined contribution plan maximum annual contribution per employee percent	4.00%	1.00%	5.00%