Retirement Benefits - Retirement Cost (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
US Plans [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	$ 0	$ 0	$ 0
Interest cost	46.2	46.5	47.7
Return on assets - expected	(65.0)	(66.8)	(61.2)
Amortization of losses	28.2	19.5	9.1
Net periodic pension cost (credit)	9.4	(0.8)	(4.1)
Non-US Plans [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	10.2	6.6	6.1
Interest cost	16.9	13.4	12.2
Return on assets - expected	(12.0)	(10.6)	(9.0)
Amortization of losses	4.3	3.2	3.5
Net periodic pension cost (credit)	21.6	12.7	12.8
UMWA plans [Member]
Net periodic pension cost (credit) [Line Items]
Interest cost	24.0	27.1	25.8
Return on assets - expected	(25.5)	(25.3)	(22.6)
Amortization of losses	14.7	16.0	16.7
Net periodic pension cost (credit)	13.2	17.8	19.9
Black lung and other plans - postretirement medical [Member]
Net periodic pension cost (credit) [Line Items]
Interest cost	2.8	2.9
Pension plan [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	10.2	6.6	6.1
Interest cost	63.1	59.9	59.9
Return on assets - expected	(77.0)	(77.4)	(70.2)
Amortization of losses	32.5	22.7	12.6
Net periodic pension cost (credit)	31.0	11.9	8.7
Retirement benefits other than pension [Member]
Net periodic pension cost (credit) [Line Items]
Interest cost	26.8	30.0	28.6
Return on assets - expected	(25.5)	(25.3)	(22.6)
Amortization of losses	17.3	17.8	16.8
Net periodic pension cost (credit)	$ 18.6	$ 22.5	$ 22.8