Loans and Related Allowance for Credit Losses (Aging Analysis) (Details) $ in Millions	Sep. 30, 2023 USD ($)
Financing Receivable [Line Items]
Financing receivable, aging analysis	$ 1,946
Current or Less Than 30 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	1,595
30-59 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	5
60-89 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	3
90 Days or More Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	9
Nonperforming Loans
Financing Receivable [Line Items]
Financing receivable, aging analysis	334
Total commercial
Financing Receivable [Line Items]
Financing receivable, aging analysis	1,782
Total commercial | Current or Less Than 30 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	1,556
Total commercial | 60-89 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis
Total commercial | 90 Days or More Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	3
Total commercial | Nonperforming Loans
Financing Receivable [Line Items]
Financing receivable, aging analysis	223
Total commercial | Commercial and industrial
Financing Receivable [Line Items]
Financing receivable, aging analysis	960
Total commercial | Commercial and industrial | Current or Less Than 30 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	801
Total commercial | Commercial and industrial | 60-89 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis
Total commercial | Commercial and industrial | 90 Days or More Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	3
Total commercial | Commercial and industrial | Nonperforming Loans
Financing Receivable [Line Items]
Financing receivable, aging analysis	156
Total commercial | Commercial real estate
Financing Receivable [Line Items]
Financing receivable, aging analysis	822
Total commercial | Commercial real estate | Current or Less Than 30 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	755
Total commercial | Commercial real estate | Nonperforming Loans
Financing Receivable [Line Items]
Financing receivable, aging analysis	67
Total consumer
Financing Receivable [Line Items]
Financing receivable, aging analysis	164
Total consumer | Current or Less Than 30 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	39
Total consumer | 30-59 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	5
Total consumer | 60-89 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	3
Total consumer | 90 Days or More Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	6
Total consumer | Nonperforming Loans
Financing Receivable [Line Items]
Financing receivable, aging analysis	111
Total consumer | Residential real estate
Financing Receivable [Line Items]
Financing receivable, aging analysis	93
Total consumer | Residential real estate | Current or Less Than 30 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	4
Total consumer | Residential real estate | 30-59 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	1
Total consumer | Residential real estate | Nonperforming Loans
Financing Receivable [Line Items]
Financing receivable, aging analysis	88
Total consumer | Home equity
Financing Receivable [Line Items]
Financing receivable, aging analysis	22
Total consumer | Home equity | Current or Less Than 30 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	1
Total consumer | Home equity | Nonperforming Loans
Financing Receivable [Line Items]
Financing receivable, aging analysis	21
Total consumer | Credit card
Financing Receivable [Line Items]
Financing receivable, aging analysis	45
Total consumer | Credit card | Current or Less Than 30 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	31
Total consumer | Credit card | 30-59 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	4
Total consumer | Credit card | 60-89 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	3
Total consumer | Credit card | 90 Days or More Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	6
Total consumer | Credit card | Nonperforming Loans
Financing Receivable [Line Items]
Financing receivable, aging analysis	1
Total consumer | Education
Financing Receivable [Line Items]
Financing receivable, aging analysis	3
Total consumer | Education | Current or Less Than 30 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	3
Total consumer | Other consumer
Financing Receivable [Line Items]
Financing receivable, aging analysis	1
Total consumer | Other consumer | Nonperforming Loans
Financing Receivable [Line Items]
Financing receivable, aging analysis	$ 1