Retirement Benefits - Retirement Cost (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
US Plans [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	$ 0	$ 0
Interest cost	11.4	10.6
Return on assets - expected	(15.4)	(14.2)
Amortization of losses	7.2	11.3
Amortization of prior service cost	0	0
Settlement loss	0	0
Net periodic pension cost	3.2	7.7
Non-US Plans [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	3.5	3.6
Interest cost	5.8	4.8
Return on assets - expected	(3.8)	(3.2)
Amortization of losses	0.5	1.6
Amortization of prior service cost	0.2	0.6
Settlement loss	0.7	0.3
Net periodic pension cost	6.9	7.7
UMWA Plans Postretirement Medical [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	0	0
Interest cost	4.8	5.0
Return on assets - expected	(5.6)	(5.2)
Amortization of losses	3.7	5.0
Amortization of prior service cost	(1.1)	0
Net periodic pension cost	1.8	4.8
Black Lung And Other Plans Postretirement Medical [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	0	0.1
Interest cost	0.6	0.5
Return on assets - expected	0	0
Amortization of losses	0.2	0.1
Amortization of prior service cost	0.4	0.4
Net periodic pension cost	1.2	1.1
Pension plan [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	3.5	3.6
Interest cost	17.2	15.4
Return on assets - expected	(19.2)	(17.4)
Amortization of losses	7.7	12.9
Amortization of prior service cost	0.2	0.6
Settlement loss	0.7	0.3
Net periodic pension cost	10.1	15.4
Retirement benefits other than pension [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	0	0.1
Interest cost	5.4	5.5
Return on assets - expected	(5.6)	(5.2)
Amortization of losses	3.9	5.1
Amortization of prior service cost	(0.7)	0.4
Net periodic pension cost	$ 3.0	$ 5.9