Retirement Benefits - Retirement Cost (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
US Plans [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	$ 0	$ 0	$ 0
Interest cost	42.2	43.8	46.2
Return on assets - expected	(56.9)	(60.0)	(65.0)
Amortization of losses	45.1	39.5	28.2
Amortization of prior service cost	0	0	0
Settlement loss	0.1	5.0	0
Net periodic pension cost	30.5	28.3	9.4
Non-US Plans [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	15.0	11.1	10.2
Interest cost	19.1	19.1	16.9
Return on assets - expected	(12.9)	(12.2)	(12.0)
Amortization of losses	6.1	4.0	2.8
Amortization of prior service cost	0.8	2.0	1.5
Settlement loss	2.6	3.3	2.2
Net periodic pension cost	30.7	27.3	21.6
UMWA Plans Postretirement Medical [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	0	0	0
Interest cost	19.7	22.3	24.0
Return on assets - expected	(20.8)	(21.3)	(25.5)
Amortization of losses	19.6	21.0	14.7
Amortization of prior service cost	0	0	0
Net periodic pension cost	18.5	22.0	13.2
Black Lung And Other Plans Postretirement Medical [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	0.3	0.6	0
Interest cost	1.9	2.8	2.8
Return on assets - expected	0	0	0
Amortization of losses	0.7	1.5	0.6
Amortization of prior service cost	1.7	2.0	2.0
Net periodic pension cost	4.6	6.9	5.4
Pension plan [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	15.0	11.1	10.2
Interest cost	61.3	62.9	63.1
Return on assets - expected	(69.8)	(72.2)	(77.0)
Amortization of losses	51.2	43.5	31.0
Amortization of prior service cost	0.8	2.0	1.5
Settlement loss	2.7	8.3	2.2
Net periodic pension cost	61.2	55.6	31.0
Retirement benefits other than pension [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	0.3	0.6	0
Interest cost	21.6	25.1	26.8
Return on assets - expected	(20.8)	(21.3)	(25.5)
Amortization of losses	20.3	22.5	15.3
Amortization of prior service cost	1.7	2.0	2.0
Net periodic pension cost	$ 23.1	$ 28.9	$ 18.6