Post Employment Plans - Target Asset Allocation Ranges (Details)	Dec. 31, 2017
Minimum | Equities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation, percentage	10.00%
Minimum | Bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation, percentage	20.00%
Minimum | Absolute return fund
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation, percentage	50.00%
Maximum | Equities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation, percentage	20.00%
Maximum | Bonds
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation, percentage	30.00%
Maximum | Absolute return fund
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, target allocation, percentage	60.00%