Retirement and Other Benefit Programs (Summary of Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Pensions | US
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 0.0	$ 3.7	$ 0.0	$ 7.4
Interest cost	3.9	3.9	7.8	7.8
Expected return on plan assets	(4.3)	(4.0)	(8.6)	(8.0)
Amortization of net prior service cost	0.0	0.0	0.0	0.0
Amortization of actuarial (gain)/loss	0.0	0.0	0.0	0.0
Net periodic benefit cost	(0.4)	3.6	(0.8)	7.2
Pensions | International
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	9.5	9.4	19.0	18.8
Interest cost	1.3	1.2	2.6	2.4
Expected return on plan assets	(2.0)	(1.8)	(4.0)	(3.6)
Amortization of net prior service cost	0.0	0.0	0.0	0.0
Amortization of actuarial (gain)/loss	(0.3)	0.0	(0.6)	0.9
Net periodic benefit cost	8.5	8.8	17.0	18.5
OPEB | US
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0.0	0.4	0.0	0.8
Interest cost	0.1	0.3	0.2	0.6
Expected return on plan assets	0.0	0.0	0.0	0.0
Amortization of net prior service cost	(0.2)	0.0	(0.4)	0.0
Amortization of actuarial (gain)/loss	0.0	0.0	0.0	0.0
Net periodic benefit cost	$ (0.1)	$ 0.7	$ (0.2)	$ 1.4