Retirement Benefits - Retirement Cost (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
US Plans [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	11.3	10.5	22.7	21.1
Return on assets - expected	(16.2)	(14.3)	(31.6)	(28.5)
Amortization of losses	7.0	11.4	14.2	22.7
Amortization of prior service cost	0	0	0	0
Settlement loss	0	0	0	0
Net periodic pension cost	2.1	7.6	5.3	15.3
Non-US Plans [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	3.2	3.8	6.7	7.4
Interest cost	4.6	4.8	10.4	9.6
Return on assets - expected	(3.8)	(3.2)	(7.6)	(6.4)
Amortization of losses	0.6	1.5	1.1	3.1
Amortization of prior service cost	0.2	(0.1)	0.4	0.5
Settlement loss	1.1	0.5	1.8	0.8
Net periodic pension cost	5.9	7.3	12.8	15.0
UMWA Plans Postretirement Medical [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	0	0	0	0
Interest cost	4.4	4.9	9.2	9.9
Return on assets - expected	(5.6)	(5.2)	(11.2)	(10.4)
Amortization of losses	2.9	4.8	6.6	9.8
Amortization of prior service cost	(1.2)	0	(2.3)	0
Net periodic pension cost	0.5	4.5	2.3	9.3
Black Lung And Other Plans Postretirement Medical [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	0.1	0.1	0.1	0.2
Interest cost	0.4	0.5	1.0	1.0
Return on assets - expected	0	0	0	0
Amortization of losses	0.1	0.2	0.3	0.3
Amortization of prior service cost	0.5	0.4	0.9	0.8
Net periodic pension cost	1.1	1.2	2.3	2.3
Pension plan [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	3.2	3.8	6.7	7.4
Interest cost	15.9	15.3	33.1	30.7
Return on assets - expected	(20.0)	(17.5)	(39.2)	(34.9)
Amortization of losses	7.6	12.9	15.3	25.8
Amortization of prior service cost	0.2	(0.1)	0.4	0.5
Settlement loss	1.1	0.5	1.8	0.8
Net periodic pension cost	8.0	14.9	18.1	30.3
Retirement benefits other than pension [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	0.1	0.1	0.1	0.2
Interest cost	4.8	5.4	10.2	10.9
Return on assets - expected	(5.6)	(5.2)	(11.2)	(10.4)
Amortization of losses	3.0	5.0	6.9	10.1
Amortization of prior service cost	(0.7)	0.4	(1.4)	0.8
Net periodic pension cost	$ 1.6	$ 5.7	$ 4.6	$ 11.6