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Contingencies and Commitments (Narrative) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Lease expense $ 130 $ 133  
Lease expense     $ 138
Minimum      
Estimate of possible loss 470    
Maximum      
Estimate of possible loss $ 720