Taxation - Summary of tax years open to examination by jurisdiction (Details)	12 Months Ended
	Dec. 31, 2014
United States
Income Tax Examination [Line Items]
Year under Examination	2013
United States | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2011
United States | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2014
Ireland | Minimum
Income Tax Examination [Line Items]
Year under Examination	2006
Open Tax Year	2006
Ireland | Maximum
Income Tax Examination [Line Items]
Year under Examination	2009
Open Tax Year	2014
United Kingdom | Minimum
Income Tax Examination [Line Items]
Year under Examination	2007
Open Tax Year	2012
United Kingdom | Maximum
Income Tax Examination [Line Items]
Year under Examination	2010
Open Tax Year	2014
Germany | Minimum
Income Tax Examination [Line Items]
Year under Examination	2006
Open Tax Year	2007
Germany | Maximum
Income Tax Examination [Line Items]
Year under Examination	2009
Open Tax Year	2014
Switzerland | Minimum
Income Tax Examination [Line Items]
Year under Examination	2009
Open Tax Year	2009
Switzerland | Maximum
Income Tax Examination [Line Items]
Year under Examination	2010
Open Tax Year	2014
France | Minimum
Income Tax Examination [Line Items]
Open Tax Year	2012
France | Maximum
Income Tax Examination [Line Items]
Open Tax Year	2014