Contingent matters - Narrative (Details) $ in Millions	Oct. 22, 2014 appeal	Sep. 17, 2014 USD ($)	Dec. 06, 2013 USD ($)	Oct. 28, 2010 USD ($)	Mar. 31, 2016 USD ($)
Loss Contingencies [Line Items]
Damages awarded (less than)				$ 1
Litigation settlement amount		$ 2	$ 7
Amount accrued					$ 2
Del Valle Gurria S.C. v. Servicio Pan Americano de Protección, S.A. de C.V
Loss Contingencies [Line Items]
Number of appeals | appeal	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 | appeal	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 | appeal	1
Maximum
Loss Contingencies [Line Items]
Company best estimate of exposure					$ 10