Pension and Post-retirement and Other Benefit Plans - Weighted-average Assumptions Used to Determine Benefit Obligations (Details)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pensions
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.48%	4.00%	4.40%
Rate of compensation increase	3.10%	3.09%	3.19%
Other post-retirement benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.73%	4.30%	4.60%