Postretirement Benefits Other Than Pensions - Actuarial Assumptions of OPEB Accumulated Benefit Obligation (Details) - Other Postretirement Benefit Plan, Defined Benefit [Member]	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	4.02%	3.36%
Rate of Increase in Future Compensation Levels	2.20%	2.20%