Derivative And Credit-Related Financial Instruments (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Cash received as collateral for derivative assets	$ 133		$ 133
Fair value of securities pledged as collateral for derivative assets	51		51
Cash posted as collateral for derivative liabilities	37		37
Aggregate fair value of all derivative instruments with credit-risk contingent features that were in a liability position	0		0
Net gain on open foreign currency positions	0	$ 0	0	$ 0
Allowance for credit losses on lending-related commitments	60		60		$ 31
Allowance for credit losses on lending-related commitments, amount related to unused commitments to extend credit	50		$ 50		25
Final year of expiration for outstanding letters of credit			2028
Risk participation agreements covering standby and commercial letters of credit	169		$ 169		161
Standby and commercial letters of credit	3,200		3,200		3,300
Carrying value of standby and commercial letters of credit included in accrued expenses and other liabilities	35		35		32
Deferred fees on standby and commercial letters of credit included in accrued expenses and other liabilities	25		25		26
Allowance for credit losses on lending-related commitments, amount related to standby and commercial letters of credit	10		10		6
Notional amount of derivative credit risk participation agreements	1,100		1,100		786
Maximum estimated exposure to credit risk participation agreements assuming 100% default	71		$ 71		20
Weighted average remaining maturity of credit risk participation agreements, in years			4 years 6 months
Fair value amount of derivative credit risk participation agreements	$ 3		$ 3		$ 0