Postretirement Benefits Other than Pensions - Discount Rate to Determine the Benefit Obligation (Details)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate (as a percent)	3.83%	3.15%	3.47%