Retirement Benefits - Retirement Cost (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
US Plans [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	$ 0	$ 0	$ 0
Interest cost	43.8	46.2	46.5
Return on assets - expected	(60.0)	(65.0)	(66.8)
Amortization of losses	39.5	28.2	19.5
Amortization of prior service cost	0	0	0
Settlement loss	5.0	0	0
Net periodic pension cost	28.3	9.4	(0.8)
Non-US Plans [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	11.1	10.2	6.6
Interest cost	19.1	16.9	13.4
Return on assets - expected	(12.2)	(12.0)	(10.6)
Amortization of losses	4.0	2.8	1.9
Amortization of prior service cost	2.0	1.5	1.3
Settlement loss	3.3	2.2	0.1
Net periodic pension cost	27.3	21.6	12.7
UMWA Plans Postretirement Medical [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	0	0	0
Interest cost	22.3	24.0	27.1
Return on assets - expected	(21.3)	(25.5)	(25.3)
Amortization of losses	21.0	14.7	16.0
Amortization of prior service cost	0	0	0
Net periodic pension cost	22.0	13.2	17.8
Black Lung And Other Plans Postretirement Medical [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	0.6	0	0
Interest cost	2.8	2.8	2.9
Return on assets - expected	0	0	0
Amortization of losses	1.5	0.6	0.4
Amortization of prior service cost	2.0	2.0	1.4
Net periodic pension cost	6.9	5.4	4.7
Pension plan [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	11.1	10.2	6.6
Interest cost	62.9	63.1	59.9
Return on assets - expected	(72.2)	(77.0)	(77.4)
Amortization of losses	43.5	31.0	21.4
Amortization of prior service cost	2.0	1.5	1.3
Settlement loss	8.3	2.2	0.1
Net periodic pension cost	55.6	31.0	11.9
Retirement benefits other than pension [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	0.6	0	0
Interest cost	25.1	26.8	30.0
Return on assets - expected	(21.3)	(25.5)	(25.3)
Amortization of losses	22.5	15.3	16.4
Amortization of prior service cost	2.0	2.0	1.4
Net periodic pension cost	$ 28.9	$ 18.6	$ 22.5