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Pension and Other Postretirement Benefit Plans - Retirement Plan Weighted Average Asset Allocations (Details) - Retirement Plan [Member]
Dec. 31, 2019
Dec. 31, 2018
Equity Securities [Member]    
Weighted average asset allocation 0.00% 0.00%
Debt Securities [Member]    
Weighted average asset allocation 100.00% 100.00%