Segment information - Narrative (Details) $ in Millions	1 Months Ended		3 Months Ended				9 Months Ended		12 Months Ended
	Dec. 31, 2014 Region Segment employee	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) Country Region employee	Jun. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) Country Region Segment	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) Region	Feb. 28, 2015 VEF / $	Mar. 31, 2014 VEF / $
Segment Reporting Information [Line Items]
Number of operating segments | Segment	9						9
Number of countries in which the entity operates, within the five largest markets	5		5				5		5
Number of regions in which the entity operates, within global markets | Region	3		3				3		3
Venezuela impairment			$ 0.8	$ 34.5			$ 35.3	$ 0.0
Restructuring Costs [Abstract]
Other divestiture gains					$ 0.6
Share-based compensation adj.			13.5		8.9		37.8	27.6
Venezuelan bolívar fuerte | Minimum
Segment Reporting Information [Line Items]
Remeasurement rate | VEF / $										52	6.3
Venezuelan bolívar fuerte | Maximum
Segment Reporting Information [Line Items]
Remeasurement rate | VEF / $										170	50
2015 Reorganization and Restructuring
Restructuring Costs [Abstract]
Restructuring cost			$ 2.0
2015 Reorganization and Restructuring | Minimum
Restructuring Costs [Abstract]
Positions eliminated across the global workforce | employee			1,000
Additional restructuring costs			$ 8.0				8.0
Expected cost savings			$ 25.0
2015 Reorganization and Restructuring | Maximum
Restructuring Costs [Abstract]
Positions eliminated across the global workforce | employee			1,200
Additional restructuring costs			$ 12.0				12.0
Expected cost savings			35.0
2014 Reorganization and Restructuring | Latin American And EMEA Regions
Restructuring Costs [Abstract]
Positions eliminated across the global workforce | employee	1,700
Severance costs									$ 21.8
Charges related to severance and lease terminations							1.2
Other items not allocated to segments
Segment Reporting Information [Line Items]
Venezuela impairment			0.8				35.3
Restructuring Costs [Abstract]
Share-based compensation adj.					$ 1.8	$ (4.2)		$ (2.4)
Other items not allocated to segments | 2015 Reorganization and Restructuring
Restructuring Costs [Abstract]
Restructuring cost			2.0				2.0
Other items not allocated to segments | 2014 Reorganization and Restructuring
Restructuring Costs [Abstract]
Restructuring cost			$ 0.9				$ 1.2
CIT Business in Peru
Restructuring Costs [Abstract]
Divestiture gains		$ 44.3