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Pension benefits (Details 4)
Dec. 31, 2018
Dec. 31, 2017
Maximum [Member]    
Discount rate 12.17% 10.60%
Rate of increase in compensation level 7.00% 7.00%
Minimum [Member]    
Discount rate 7.25% 5.78%
Rate of increase in compensation level 5.00% 5.00%