Loans and Related Allowance for Credit Losses (Aging Analysis) (Details) $ in Millions	Mar. 31, 2023 USD ($)
Financing Receivable [Line Items]
Financing receivable, aging analysis	$ 623
Current or Less Than 30 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	581
30-59 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	19
60-89 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	5
90 Days Or More Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	18
Total commercial
Financing Receivable [Line Items]
Financing receivable, aging analysis	497
Total commercial | Current or Less Than 30 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	491
Nonaccrual, aging analysis	49
Total commercial | 30-59 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	5
Total commercial | 60-89 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	1
Total commercial | 30 Days or More Past Due
Financing Receivable [Line Items]
Nonaccrual, aging analysis	5
Total commercial | Commercial and industrial
Financing Receivable [Line Items]
Financing receivable, aging analysis	224
Total commercial | Commercial and industrial | Current or Less Than 30 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	218
Total commercial | Commercial and industrial | 30-59 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	5
Total commercial | Commercial and industrial | 60-89 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	1
Total commercial | Commercial real estate
Financing Receivable [Line Items]
Financing receivable, aging analysis	273
Total commercial | Commercial real estate | Current or Less Than 30 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	273
Total consumer
Financing Receivable [Line Items]
Financing receivable, aging analysis	126
Total consumer | Current or Less Than 30 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	90
Nonaccrual, aging analysis	18
Total consumer | 30-59 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	14
Total consumer | 60-89 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	4
Total consumer | 90 Days Or More Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	18
Total consumer | 30 Days or More Past Due
Financing Receivable [Line Items]
Nonaccrual, aging analysis	23
Total consumer | Residential real estate
Financing Receivable [Line Items]
Financing receivable, aging analysis	49
Total consumer | Residential real estate | Current or Less Than 30 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	24
Total consumer | Residential real estate | 30-59 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	10
Total consumer | Residential real estate | 60-89 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	2
Total consumer | Residential real estate | 90 Days Or More Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	13
Total consumer | Home equity
Financing Receivable [Line Items]
Financing receivable, aging analysis	5
Total consumer | Home equity | Current or Less Than 30 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	4
Total consumer | Home equity | 90 Days Or More Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	1
Total consumer | Credit card
Financing Receivable [Line Items]
Financing receivable, aging analysis	13
Total consumer | Credit card | Current or Less Than 30 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	7
Total consumer | Credit card | 30-59 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	2
Total consumer | Credit card | 60-89 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	2
Total consumer | Credit card | 90 Days Or More Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	2
Total consumer | Education
Financing Receivable [Line Items]
Financing receivable, aging analysis	58
Total consumer | Education | Current or Less Than 30 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	54
Total consumer | Education | 30-59 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	2
Total consumer | Education | 90 Days Or More Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	2
Total consumer | Other consumer
Financing Receivable [Line Items]
Financing receivable, aging analysis	1
Total consumer | Other consumer | Current or Less Than 30 Days Past Due
Financing Receivable [Line Items]
Financing receivable, aging analysis	$ 1