Retirement Benefits - Retirement Cost (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
US Plans [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	11.3	10.6	34.0	31.7
Return on assets - expected	(16.2)	(14.2)	(47.8)	(42.7)
Amortization of losses	7.0	11.2	21.2	33.9
Amortization of prior service cost	0	0	0	0
Settlement loss	0	0	0	0
Net periodic cost	2.1	7.6	7.4	22.9
Non-US Plans [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	3.1	3.7	9.8	11.1
Interest cost	4.5	4.7	14.9	14.3
Return on assets - expected	(3.7)	(3.2)	(11.3)	(9.6)
Amortization of losses	0.6	1.5	1.7	4.6
Amortization of prior service cost	0.2	0.2	0.6	0.7
Settlement loss	2.4	0.8	4.2	1.6
Net periodic cost	7.1	7.7	19.9	22.7
UMWA Plans Postretirement Medical [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	0	0	0	0
Interest cost	4.4	4.9	13.6	14.8
Return on assets - expected	(5.6)	(5.2)	(16.8)	(15.6)
Amortization of losses	2.9	4.9	9.5	14.7
Amortization of prior service cost	(1.2)	0	(3.5)	0
Net periodic cost	0.5	4.6	2.8	13.9
Black Lung And Other Plans Postretirement Medical [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	0	0	0.1	0.2
Interest cost	0.6	0.5	1.6	1.5
Return on assets - expected	0	0	0	0
Amortization of losses	0.2	0.2	0.5	0.5
Amortization of prior service cost	0.4	0.5	1.3	1.3
Net periodic cost	1.2	1.2	3.5	3.5
Pension plan [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	3.1	3.7	9.8	11.1
Interest cost	15.8	15.3	48.9	46.0
Return on assets - expected	(19.9)	(17.4)	(59.1)	(52.3)
Amortization of losses	7.6	12.7	22.9	38.5
Amortization of prior service cost	0.2	0.2	0.6	0.7
Settlement loss	2.4	0.8	4.2	1.6
Net periodic cost	9.2	15.3	27.3	45.6
Retirement benefits other than pension [Member]
Net periodic pension cost (credit) [Line Items]
Service cost	0	0	0.1	0.2
Interest cost	5.0	5.4	15.2	16.3
Return on assets - expected	(5.6)	(5.2)	(16.8)	(15.6)
Amortization of losses	3.1	5.1	10.0	15.2
Amortization of prior service cost	(0.8)	0.5	(2.2)	1.3
Net periodic cost	$ 1.7	$ 5.8	$ 6.3	$ 17.4