Retirement Benefits - Retirement Cost (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
US Plans [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	$ 0	$ 0
Interest cost	10.6	11.0
Return on assets - expected	(14.2)	(15.1)
Amortization of losses	11.3	10.0
Amortization of prior service cost	0	0
Settlement loss	0	4.0
Net periodic pension cost	7.7	9.9
Non-US Plans [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	3.6	2.6
Interest cost	4.8	4.1
Return on assets - expected	(3.2)	(3.0)
Amortization of losses	1.6	1.1
Amortization of prior service cost	0.6	0.4
Settlement loss	0.3	0.8
Net periodic pension cost	7.7	6.0
UMWA Plans Postretirement Medical [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	0	0
Interest cost	5.0	5.6
Return on assets - expected	(5.2)	(5.3)
Amortization of losses	5.0	5.4
Amortization of prior service cost	0	0
Net periodic pension cost	4.8	5.7
Black Lung And Other Plans Postretirement Medical [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	0.1	0
Interest cost	0.5	0.8
Return on assets - expected	0	0
Amortization of losses	0.1	0.2
Amortization of prior service cost	0.4	0.5
Net periodic pension cost	1.1	1.5
Pension plan [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	3.6	2.6
Interest cost	15.4	15.1
Return on assets - expected	(17.4)	(18.1)
Amortization of losses	12.9	11.1
Amortization of prior service cost	0.6	0.4
Settlement loss	0.3	4.8
Net periodic pension cost	15.4	15.9
Retirement benefits other than pension [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	0.1	0
Interest cost	5.5	6.4
Return on assets - expected	(5.2)	(5.3)
Amortization of losses	5.1	5.6
Amortization of prior service cost	0.4	0.5
Net periodic pension cost	$ 5.9	$ 7.2