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Commitments (Narrative) (Details)
$ in Billions
12 Months Ended
Dec. 31, 2020
USD ($)
Standby letters of credit  
Loss Contingencies [Line Items]  
Internal credit ratings (as a percentage of portfolio) - Pass 96.00%
Standby letters of credit - Assets securing certain specifically identified standby letters of credit $ 1.1
Standby letters of credit and participations in standby letters of credit - Liability carrying amount $ 0.2
Less than 1 year  
Loss Contingencies [Line Items]  
Standby letters of credit, term 1 year
Maximum  
Loss Contingencies [Line Items]  
Standby letters of credit, term 6 years