Pension benefits (Details 3)	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	5.40%	5.00%	4.70%
Rate of increase in compensation level	5.00%	6.00%	6.00%
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	12.50%	9.80%	9.50%
Rate of increase in compensation level	8.50%	9.00%	9.00%