Derivative And Credit-Related Financial Instruments (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Effects of fair value hedging on the Consolidated Statements o Comprehensive Income [Line Items]
Fair value of securities pledged as collateral for derivative liabilities	$ 10		$ 10
Cash received as collateral for derivative assets	8		8
Fair value of securities received as collateral for derivative assets	4		4
Cash posted as collateral for derivative liabilities	173		173
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	33		33		$ 42
Allowance for credit losses on lending-related commitments, amount related to unused commitments to extend credit	25		$ 25		27
Final year of expiration for outstanding letters of credit			2028
Risk participation agreements covering standby and commercial letters of credit	136		$ 136		127
Standby and commercial letters of credit	3,300		3,300		3,300
Carrying value of standby and commercial letters of credit included in accrued expenses and other liabilities	33		33		40
Deferred fees on standby and commercial letters of credit included in accrued expenses and other liabilities	25		25		25
Allowance for credit losses on lending-related commitments, amount related to standby and commercial letters of credit	8		8		15
Notional amount of derivative credit risk participation agreements	631		631		549
Maximum estimated exposure to credit risk participation agreements assuming 100% default	$ 2		$ 2		$ 0
Weighted average remaining maturity of credit risk participation agreements, in years			3 years 3 months 18 days