Derivative And Credit-Related Financial Instruments (Summary Of Criticized Letters Of Credit) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Document Period End Date	Dec. 31, 2019
Total criticized standby and commercial letters of credit	$ 44	$ 49
As a percentage of total outstanding standby and commercial letters of credit	1.30%	1.50%

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