Credit Quality And Allowance For Credit Losses (Troubled Debt Restructurings By Type Of Modification) (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
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring, Postmodification		$ 13	$ 11	$ 29	$ 20
Commitments to lend additional funds to TDR borrowers		1		1		$ 3
Business loans | Commercial borrower
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring, Postmodification		12	11	28	19
Business loans | Commercial borrower | Domestic loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring, Postmodification		11	11	26	19
Business loans | Commercial mortgage | Commercial borrower | Domestic loans | Other business lines
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring, Postmodification	[1]	1	0	2	0
Retail | Retail | Domestic loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring, Postmodification	[2]	1	0	1	1
Principal Deferrals
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring, Postmodification	[3]	12	11	28	19
Subsequent default during period		6	17	11	17
Principal Deferrals | Business loans | Commercial borrower
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring, Postmodification		12	11	28	19
Principal Deferrals | Business loans | Commercial borrower | Domestic loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring, Postmodification	[3]	11	11	26	19
Principal Deferrals | Business loans | Commercial mortgage | Commercial borrower | Domestic loans | Other business lines
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring, Postmodification	[1],[3]	1	0	2	0
Principal Deferrals | Retail | Retail | Domestic loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring, Postmodification	[2],[3]	0	0	0	0
Interest Rate Reductions
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring, Postmodification		1	0	1	1
Subsequent default during period		0	0	0	0
Interest Rate Reductions | Business loans | Commercial borrower
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring, Postmodification		0	0	0	0
Interest Rate Reductions | Business loans | Commercial borrower | Domestic loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring, Postmodification		0	0	0	0
Interest Rate Reductions | Business loans | Commercial mortgage | Commercial borrower | Domestic loans | Other business lines
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring, Postmodification	[1]	0	0	0	0
Interest Rate Reductions | Retail | Retail | Domestic loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing Receivable, Troubled Debt Restructuring, Postmodification	[2]	$ 1	$ 0	$ 1	$ 1

[1] Primarily loans secured by owner-occupied real estate.

[2] Includes bankruptcy loans for which the court has discharged the borrower's obligation and the borrower has not reaffirmed the debt.

[3] Primarily represents loan balances where terms were extended by more than an insignificant time period, typically more than 180 days, at or above contractual interest rates. Also includes commercial loans restructured in bankruptcy.