Taxation - Summary of tax years open to examination by jurisdiction (Details)	12 Months Ended
	Dec. 31, 2016
United States | Minimum
Income Tax Examination [Line Items]
Year under Examination	2013
Open Tax Year	2013
United States | Maximum
Income Tax Examination [Line Items]
Year under Examination	2015
Open Tax Year	2016
Ireland | Minimum
Income Tax Examination [Line Items]
Year under Examination	2008
Open Tax Year	2008
Ireland | Maximum
Income Tax Examination [Line Items]
Year under Examination	2009
Open Tax Year	2016
United Kingdom
Income Tax Examination [Line Items]
Year under Examination	2014
United Kingdom | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2014
United Kingdom | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2016
Germany | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2014
Germany | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2016
Switzerland | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2011
Switzerland | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2016
France | Minimum
Income Tax Examination [Line Items]
Year under Examination	2013
Open Tax Year	2013
France | Maximum
Income Tax Examination [Line Items]
Year under Examination	2014
Open Tax Year	2016
Spain | Minimum
Income Tax Examination [Line Items]
Year under Examination	2011
Open Tax Year	2011
Spain | Maximum
Income Tax Examination [Line Items]
Year under Examination	2012
Open Tax Year	2016
Italy | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2012
Italy | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2016