Retirement and Other Benefit Programs (Change in Benefit Obligations and Fair Value of Plan Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Pensions
Benefit obligations
Beginning of period	$ 965.5
End of Period	1,061.5	$ 965.5
Fair value of plan assets
Beginning of period	426.3
End of Period	496.9	426.3
Pensions | International
Benefit obligations
Beginning of period	581.4	0.0
Assumption of benefit obligations	0.0	503.8
Service cost	39.4	18.6
Interest cost	4.9	3.2
Participant contributions	8.9	3.2
Actuarial loss/(gain)	(22.9)	(29.8)
Benefit payments	(19.8)	(9.1)
Plan amendments	0.0	0.0
Settlements	(10.4)	(3.2)
Curtailments	(4.0)	0.0
Foreign exchange	45.4	(18.3)
Other	(5.0)	113.0
End of Period	617.9	581.4
Fair value of plan assets
Beginning of period	197.9	0.0
Assumption of plan assets	0.0	140.5
Actual return on plan assets	12.3	2.0
Employer contributions	32.2	12.3
Participant contributions	8.9	3.2
Benefit payments	(19.8)	(9.1)
Settlements	(10.4)	(3.2)
Foreign exchange	11.9	(3.8)
Other	4.2	56.0
End of Period	237.2	197.9
Funded status	(380.7)	(383.5)
Other current liabilities	(15.7)	(8.8)
Other non-current liabilities	(365.0)	(374.7)
Net liability recognized	(380.7)	(383.5)
Pensions | US
Benefit obligations
Beginning of period	384.1	0.0
Assumption of benefit obligations	0.0	441.6
Service cost	14.6	13.0
Interest cost	15.6	11.1
Participant contributions	0.0	0.0
Actuarial loss/(gain)	34.4	(10.6)
Benefit payments	(5.1)	(1.6)
Plan amendments	0.0	0.0
Settlements	0.0	0.0
Curtailments	0.0	(73.4)
Foreign exchange	0.0	0.0
Other	0.0	4.0
End of Period	443.6	384.1
Fair value of plan assets
Beginning of period	228.4	0.0
Assumption of plan assets	0.0	218.0
Actual return on plan assets	35.4	8.3
Employer contributions	0.9	0.4
Participant contributions	0.0	0.0
Benefit payments	(5.0)	(1.6)
Settlements	0.0	0.0
Foreign exchange	0.0	0.0
Other	0.0	3.3
End of Period	259.7	228.4
Funded status	(183.9)	(155.7)
Other current liabilities	(0.8)	(0.6)
Other non-current liabilities	(183.1)	(155.1)
Net liability recognized	(183.9)	(155.7)
OPEB | US
Benefit obligations
Beginning of period	25.0	0.0
Assumption of benefit obligations	0.0	23.5
Service cost	1.5	0.8
Interest cost	1.0	0.6
Participant contributions	0.0	0.0
Actuarial loss/(gain)	(1.2)	0.1
Benefit payments	(0.2)	0.0
Plan amendments	(9.0)	0.0
Settlements	0.0	0.0
Curtailments	0.0	0.0
Foreign exchange	0.0	0.0
Other	0.0	0.0
End of Period	17.1	25.0
Fair value of plan assets
Beginning of period	0.0	0.0
Assumption of plan assets	0.0	0.0
Actual return on plan assets	0.0	0.0
Employer contributions	0.2	0.0
Participant contributions	0.0	0.0
Benefit payments	(0.2)	0.0
Settlements	0.0	0.0
Foreign exchange	0.0	0.0
Other	0.0	0.0
End of Period	0.0	0.0
Funded status	(17.1)	(25.0)
Other current liabilities	(0.4)	(0.2)
Other non-current liabilities	(16.7)	(24.8)
Net liability recognized	$ (17.1)	$ (25.0)