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Postretirement Benefits Other Than Pensions - Actuarial Assumptions of OPEB Accumulated Benefit Obligation (Details) - Other Postretirement Benefit Plan, Defined Benefit
Dec. 31, 2019
Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]    
Discount Rate 2.91% 4.02%
Rate of Increase in Future Compensation Levels 2.20% 2.20%