Retirement Benefits - Retirement Cost (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
US Plans [Member]    
Net periodic pension cost (credit) [Line Items]    
Service cost $ 0 $ 0
Interest cost on projected benefit obligation 9.0 11.4
Return on assets - expected (13.7) (15.4)
Amortization of losses 7.8 7.2
Amortization of prior service cost 0 0
Settlement loss 0 0
Net periodic pension cost 3.1 3.2
US Plans [Member] | Continuing Operations [Member]    
Net periodic pension cost (credit) [Line Items]    
Net periodic pension cost 3.1 3.2
US Plans [Member] | Discontinued Operations [Member]    
Net periodic pension cost (credit) [Line Items]    
Net periodic pension cost 0 0
Non-US Plans [Member]    
Net periodic pension cost (credit) [Line Items]    
Service cost 2.9 3.5
Interest cost on projected benefit obligation 3.2 5.8
Return on assets - expected (2.4) (3.8)
Amortization of losses 1.3 0.5
Amortization of prior service cost 0 0.2
Settlement loss 2.3 0.7
Net periodic pension cost 7.3 6.9
Non-US Plans [Member] | Continuing Operations [Member]    
Net periodic pension cost (credit) [Line Items]    
Net periodic pension cost 6.2 6.5
Non-US Plans [Member] | Discontinued Operations [Member]    
Net periodic pension cost (credit) [Line Items]    
Net periodic pension cost 1.1 0.4
UMWA Plans Postretirement Medical [Member]    
Net periodic pension cost (credit) [Line Items]    
Service cost 0 0
Interest cost on projected benefit obligation 4.5 4.8
Return on assets - expected (5.2) (5.6)
Amortization of losses 4.3 3.7
Amortization of prior service cost (1.2) (1.1)
Net periodic pension cost 2.4 1.8
Black Lung And Other Plans Postretirement Medical [Member]    
Net periodic pension cost (credit) [Line Items]    
Service cost 0 0
Interest cost on projected benefit obligation 0.7 0.6
Return on assets - expected 0 0
Amortization of losses 0.7 0.2
Amortization of prior service cost 0.5 0.4
Net periodic pension cost 1.9 1.2
Pension plan [Member]    
Net periodic pension cost (credit) [Line Items]    
Service cost 2.9 3.5
Interest cost on projected benefit obligation 12.2 17.2
Return on assets - expected (16.1) (19.2)
Amortization of losses 9.1 7.7
Amortization of prior service cost 0 0.2
Settlement loss 2.3 0.7
Net periodic pension cost 10.4 10.1
Pension plan [Member] | Continuing Operations [Member]    
Net periodic pension cost (credit) [Line Items]    
Net periodic pension cost 9.3 9.7
Pension plan [Member] | Discontinued Operations [Member]    
Net periodic pension cost (credit) [Line Items]    
Net periodic pension cost 1.1 0.4
Retirement benefits other than pension [Member]    
Net periodic pension cost (credit) [Line Items]    
Service cost 0 0
Interest cost on projected benefit obligation 5.2 5.4
Return on assets - expected (5.2) (5.6)
Amortization of losses 5.0 3.9
Amortization of prior service cost (0.7) (0.7)
Net periodic pension cost $ 4.3 $ 3.0