Loans And Allowance For Credit Losses (Schedule Of Investment Of Accruing And Nonaccruing Loans Modified As Troubled Debt Restructurings) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 18	$ 7	$ 129	$ 180
Accruing [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	4
Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	18	3
Commercial And Industrial [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	14	3
Commercial And Industrial [Member] | Accruing [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	0
Commercial And Industrial [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	14	3
Owner Occupied [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	2	4
Owner Occupied [Member] | Accruing [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	4
Owner Occupied [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	2	0
Commercial Loan [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	16	7
Commercial Loan [Member] | Accruing [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	4
Commercial Loan [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	16	3
Term [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	2	0
Term [Member] | Accruing [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	0
Term [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	2	0
Commercial Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	2	0
Commercial Real Estate [Member] | Accruing [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	0	0
Commercial Real Estate [Member] | Nonaccruing [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 2	$ 0