Post Employment Plans - Expected Long-term Rate of Return (Details)	12 Months Ended
	Dec. 31, 2017
Equities
Defined Benefit Plan Disclosure [Line Items]
Expected return on assets, percent	6.00%
Bonds
Defined Benefit Plan Disclosure [Line Items]
Expected return on assets, percent	1.90%
Absolute return fund
Defined Benefit Plan Disclosure [Line Items]
Expected return on assets, percent	4.00%
Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Expected return on assets, percent	2.80%
Other
Defined Benefit Plan Disclosure [Line Items]
Expected return on assets, percent	2.50%