Derivative And Credit-Related Financial Instruments (Summary Of Internally Classified Watch List Letters Of Credit) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Total criticized standby and commercial letters of credit	$ 50	$ 49
As a percentage of total outstanding standby and commercial letters of credit	1.50%	1.50%