Contingent matters - Narrative (Details) $ in Millions	Oct. 22, 2014 appeal	Sep. 17, 2014 USD ($)	Dec. 06, 2013 USD ($)	Oct. 28, 2010 USD ($)
Loss Contingencies [Line Items]
Damages awarded (less than) | $				$ 1
Litigation settlement amount | $		$ (2)	$ 7
Del Valle Gurria S.C. v. Servicio Pan Americano de Protección, S.A. de C.V
Loss Contingencies [Line Items]
Number of appeals	2
U.S. | Del Valle Gurria S.C. v. Servicio Pan Americano de Protección, S.A. de C.V
Loss Contingencies [Line Items]
Number of appeals	1
Mexico | Del Valle Gurria S.C. v. Servicio Pan Americano de Protección, S.A. de C.V
Loss Contingencies [Line Items]
Number of appeals	1