Pension and Post-retirement and Other Benefit Plans - Weighted-average Assumptions Used to Determine Net Periodic Benefit Cost (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pensions
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.98%	4.34%	4.03%
Rate of compensation increase	3.10%	3.09%	3.19%
Expected rate of return on plan assets	6.58%	6.83%	7.08%
Other post-retirement benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	4.30%	4.60%	4.25%