Fair Value Accounting - Estimated Fair Value of Financial Instruments (Detail) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Financial assets
HTM	$ 1,526	$ 1,429
AFS	13,468	11,165
Investment securities - equity	117	$ 126
Derivative Asset, Statement of Financial Position [Extensible Enumeration]		Other assets
Loans HFS	2,286	$ 1,402
Net loans HFI	53,302	49,960
Mortgage servicing rights	1,127	1,124
Accrued interest receivable	5	5
Financial liabilities
Total deposits	66,341	55,333
Other borrowings	5,573	7,230
Qualifying debt	65	63
Fair Value, Nonrecurring | Carrying Amount
Financial assets
HTM	1,526	1,429
Net loans HFI	53,302	49,960
Accrued interest receivable	362	370
Financial liabilities
Total deposits	66,341	55,333
Other borrowings	5,573	7,230
Qualifying debt	899	895
Accrued interest payable	138	151
Fair Value, Nonrecurring | Estimate of Fair Value Measurement
Financial assets
HTM	1,309	1,251
Net loans HFI	53,070	46,877
Accrued interest receivable	362	370
Financial liabilities
Total deposits	66,393	55,379
Other borrowings	5,545	7,192
Qualifying debt	867	810
Accrued interest payable	138	151
Fair Value, Nonrecurring | Estimate of Fair Value Measurement | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets
HTM	0	0
Net loans HFI	0	0
Accrued interest receivable	0	0
Financial liabilities
Total deposits	0	0
Other borrowings	0	0
Qualifying debt	0	0
Accrued interest payable	0	0
Fair Value, Nonrecurring | Estimate of Fair Value Measurement | Significant Other Observable Inputs (Level 2)
Financial assets
HTM	1,309	1,251
Net loans HFI	0	0
Accrued interest receivable	362	370
Financial liabilities
Total deposits	66,393	55,379
Other borrowings	5,545	7,192
Qualifying debt	789	734
Accrued interest payable	138	151
Fair Value, Nonrecurring | Estimate of Fair Value Measurement | Significant Unobservable Inputs (Level 3)
Financial assets
HTM	0	0
Net loans HFI	53,070	46,877
Accrued interest receivable	0	0
Financial liabilities
Total deposits	0	0
Other borrowings	0	0
Qualifying debt	78	76
Accrued interest payable	0	0
Fair Value, Recurring
Financial assets
AFS	13,468	11,165
Investment securities - equity	117	126
Derivative assets	233	88
Financial liabilities
Derivative liabilities	76	100
Fair Value, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets
AFS	4,385	4,881
Investment securities - equity	117	126
Derivative assets	0	0
Financial liabilities
Qualifying debt	0	0
Derivative liabilities	0	0
Fair Value, Recurring | Significant Other Observable Inputs (Level 2)
Financial assets
AFS	9,083	6,284
Investment securities - equity	0	0
Derivative assets	198	66
Financial liabilities
Qualifying debt	0	0
Derivative liabilities	69	100
Fair Value, Recurring | Significant Unobservable Inputs (Level 3)
Financial assets
AFS	0	0
Investment securities - equity	0	0
Derivative assets	35	22
Financial liabilities
Qualifying debt	65	63
Derivative liabilities	7	0
Fair Value, Recurring | Carrying Amount
Financial assets
AFS	13,468	11,165
Investment securities - equity	117	126
Derivative assets	233	84
Loans HFS	2,286	1,402
Mortgage servicing rights	1,127	1,124
Financial liabilities
Derivative liabilities	76	100
Fair Value, Recurring | Estimate of Fair Value Measurement
Financial assets
AFS	13,468	11,165
Investment securities - equity	117	126
Derivative assets	233	88
Loans HFS	2,286	1,402
Mortgage servicing rights	1,127	1,124
Financial liabilities
Derivative liabilities	76	100
Fair Value, Recurring | Estimate of Fair Value Measurement | Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets
AFS	4,385	4,881
Investment securities - equity	117	126
Derivative assets	0	0
Loans HFS	0	0
Mortgage servicing rights	0	0
Financial liabilities
Derivative liabilities	0	0
Fair Value, Recurring | Estimate of Fair Value Measurement | Significant Other Observable Inputs (Level 2)
Financial assets
AFS	9,083	6,284
Investment securities - equity	0	0
Derivative assets	198	66
Loans HFS	2,259	1,379
Mortgage servicing rights	0	0
Financial liabilities
Derivative liabilities	69	100
Fair Value, Recurring | Estimate of Fair Value Measurement | Significant Unobservable Inputs (Level 3)
Financial assets
AFS	0	0
Investment securities - equity	0	0
Derivative assets	35	22
Loans HFS	27	23
Mortgage servicing rights	1,127	1,124
Financial liabilities
Derivative liabilities	$ 7	$ 0