Loans and Allowance for Credit Losses - Summary Of Loans That Defaulted And Modified (Detail) - USD ($) $ in Millions		3 Months Ended	9 Months Ended
		Sep. 30, 2023	Sep. 30, 2023
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		$ 1,441	$ 2,946
Contractual Interest Rate Reduction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		135	310
Payment Deferral [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		525	1,262
Extended Maturity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		644	1,085
Multiple Modification [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period	[1]	137	289
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Contractual Interest Rate Reduction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		12	18
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Payment Deferral [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		24	28
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Extended Maturity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		14	16
Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Multiple Modification [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period	[2]	6	8
Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		114	249
Commercial Portfolio Segment [Member] | Contractual Interest Rate Reduction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		16	36
Commercial Portfolio Segment [Member] | Extended Maturity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		98	213
Commercial Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Contractual Interest Rate Reduction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		2	3
Residential Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		65	259
Residential Portfolio Segment [Member] | Payment Deferral [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		58	221
Residential Portfolio Segment [Member] | Extended Maturity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		6	21
Residential Portfolio Segment [Member] | Multiple Modification [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period	[1],[3]	1	17
Residential Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Payment Deferral [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		4	5
Residential Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Extended Maturity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		1	1
Residential Portfolio Segment [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Multiple Modification [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period	[2]		1
Credit Card Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		117	269
Credit Card Receivable [Member] | Contractual Interest Rate Reduction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		117	268
Credit Card Receivable [Member] | Payment Deferral [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period			1
Credit Card Receivable [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Contractual Interest Rate Reduction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		10	15
Other Retail Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		53	141
Other Retail Loans [Member] | Contractual Interest Rate Reduction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		2	6
Other Retail Loans [Member] | Payment Deferral [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		12	20
Other Retail Loans [Member] | Extended Maturity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		39	113
Other Retail Loans [Member] | Multiple Modification [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period	[1]		2
Other Retail Loans [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Extended Maturity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		4	5
Total Loans Excluding Loans Purchased Gnma Mortgage Pools [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		784	1,454
Total Loans Excluding Loans Purchased Gnma Mortgage Pools [Member] | Contractual Interest Rate Reduction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		135	310
Total Loans Excluding Loans Purchased Gnma Mortgage Pools [Member] | Payment Deferral [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		70	242
Total Loans Excluding Loans Purchased Gnma Mortgage Pools [Member] | Extended Maturity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		569	874
Total Loans Excluding Loans Purchased Gnma Mortgage Pools [Member] | Multiple Modification [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period	[1]	10	28
Total Loans Excluding Loans Purchased Gnma Mortgage Pools [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Contractual Interest Rate Reduction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		12	18
Total Loans Excluding Loans Purchased Gnma Mortgage Pools [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Payment Deferral [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		4	5
Total Loans Excluding Loans Purchased Gnma Mortgage Pools [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Extended Maturity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		5	6
Total Loans Excluding Loans Purchased Gnma Mortgage Pools [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Multiple Modification [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period	[2]		1
Loans purchased from GNMA mortgage pools [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Payment Deferral [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		20	23
Loans purchased from GNMA mortgage pools [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Extended Maturity [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period		9	10
Loans purchased from GNMA mortgage pools [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Multiple Modification [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans modified during the period	[2]	$ 6	$ 7

[1] Includes $126 million of total loans receiving a payment delay and term extension, $9 million of total loans receiving an interest rate reduction and term extension and $2 million of total loans receiving an interest rate reduction, payment delay and term extension for three months ended September 30, 2023. Includes $268 million of total loans receiving a payment delay and term extension, $14 million of total loans receiving an interest rate reduction and term extension and $7 million of total loans receiving an interest rate reduction, payment delay and term extension for nine months ended September 30, 2023.

[2] Represents loans receiving a payment delay and term extension for three months ended September 30, 2023. Includes $7 million of total loans receiving a payment delay and term extension and $1 million of total loans receiving an interest rate reduction, payment delay and term extension for the nine months ended September 30, 2023.

[3] Percent of class total amounts expressed as a percent of total residential mortgage loan balances.