Segment information Segment information - Assets by Segment (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Assets held by Segment	$ 2,289.0	$ 1,994.8
Reportable segments
Segment Reporting Information [Line Items]
Assets held by Segment	1,909.8	1,622.6
Reportable segments | North America
Segment Reporting Information [Line Items]
Assets held by Segment	726.1	629.4
Reportable segments | South America
Segment Reporting Information [Line Items]
Assets held by Segment	462.3	371.4
Reportable segments | Rest of World
Segment Reporting Information [Line Items]
Assets held by Segment	721.4	621.8
Corporate expenses
Segment Reporting Information [Line Items]
Assets held by Segment	335.7	321.3
Venezuela | Other items not allocated to segments
Segment Reporting Information [Line Items]
Assets held by Segment	$ 43.5	$ 50.9