Investment Securities - Investment Securities by Credit Rating Type (Detail) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	$ 1,526	$ 1,429
Fair value	13,468	11,165
Investment securities - equity	117	126
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Fair value	4,383	4,853
Residential MBS issued by GSEs and GNMA
Debt Securities, Available-for-sale [Line Items]
Fair value	5,831	1,972
CLO
Debt Securities, Available-for-sale [Line Items]
Fair value	570	1,399
Private label residential MBS
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	176	186
Fair value	947	1,117
Tax-exempt
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	1,350	1,243
Fair value	845	858
Commercial MBS issued by GSEs and GNMA
Debt Securities, Available-for-sale [Line Items]
Fair value	437	530
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Fair value	386	367
Other
Debt Securities, Available-for-sale [Line Items]
Fair value	69	69
Preferred Stock
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	91	100
CRA investments
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	26	26
AAA
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	0	0
Fair value	980	1,178
Investment securities - equity	0	0
AAA | U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
AAA | Residential MBS issued by GSEs and GNMA
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
AAA | CLO
Debt Securities, Available-for-sale [Line Items]
Fair value	50	79
AAA | Private label residential MBS
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	0	0
Fair value	921	1,090
AAA | Tax-exempt
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	0	0
Fair value	9	9
AAA | Commercial MBS issued by GSEs and GNMA
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
AAA | Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
AAA | Other
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
AAA | Preferred Stock
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0	0
AAA | CRA investments
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0	0
Split-rated AAA/AA+
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	0	0
Fair value	10,671	7,371
Investment securities - equity	26	26
Split-rated AAA/AA+ | U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Fair value	4,383	4,853
Split-rated AAA/AA+ | Residential MBS issued by GSEs and GNMA
Debt Securities, Available-for-sale [Line Items]
Fair value	5,831	1,972
Split-rated AAA/AA+ | CLO
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
Split-rated AAA/AA+ | Private label residential MBS
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	0	0
Fair value	0	0
Split-rated AAA/AA+ | Tax-exempt
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	0	0
Fair value	19	16
Split-rated AAA/AA+ | Commercial MBS issued by GSEs and GNMA
Debt Securities, Available-for-sale [Line Items]
Fair value	437	530
Split-rated AAA/AA+ | Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
Split-rated AAA/AA+ | Other
Debt Securities, Available-for-sale [Line Items]
Fair value	1	0
Split-rated AAA/AA+ | Preferred Stock
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0	0
Split-rated AAA/AA+ | CRA investments
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	26	26
AA+ to AA-
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	0	0
Fair value	847	1,661
Investment securities - equity	0	0
AA+ to AA- | U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
AA+ to AA- | Residential MBS issued by GSEs and GNMA
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
AA+ to AA- | CLO
Debt Securities, Available-for-sale [Line Items]
Fair value	465	1,265
AA+ to AA- | Private label residential MBS
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	0	0
Fair value	26	26
AA+ to AA- | Tax-exempt
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	0	0
Fair value	348	361
AA+ to AA- | Commercial MBS issued by GSEs and GNMA
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
AA+ to AA- | Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
AA+ to AA- | Other
Debt Securities, Available-for-sale [Line Items]
Fair value	8	9
AA+ to AA- | Preferred Stock
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0	0
AA+ to AA- | CRA investments
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0	0
A+ to A-
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	0	0
Fair value	510	528
Investment securities - equity	0	0
A+ to A- | U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
A+ to A- | Residential MBS issued by GSEs and GNMA
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
A+ to A- | CLO
Debt Securities, Available-for-sale [Line Items]
Fair value	55	55
A+ to A- | Private label residential MBS
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	0	0
Fair value	0	0
A+ to A- | Tax-exempt
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	0	0
Fair value	375	386
A+ to A- | Commercial MBS issued by GSEs and GNMA
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
A+ to A- | Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Fair value	78	76
A+ to A- | Other
Debt Securities, Available-for-sale [Line Items]
Fair value	2	11
A+ to A- | Preferred Stock
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0	0
A+ to A- | CRA investments
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0	0
BBB+ to BBB-
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	0	0
Fair value	266	239
Investment securities - equity	50	54
BBB+ to BBB- | U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
BBB+ to BBB- | Residential MBS issued by GSEs and GNMA
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
BBB+ to BBB- | CLO
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
BBB+ to BBB- | Private label residential MBS
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	0	0
Fair value	0	0
BBB+ to BBB- | Tax-exempt
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	0	0
Fair value	0	0
BBB+ to BBB- | Commercial MBS issued by GSEs and GNMA
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
BBB+ to BBB- | Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Fair value	226	211
BBB+ to BBB- | Other
Debt Securities, Available-for-sale [Line Items]
Fair value	40	28
BBB+ to BBB- | Preferred Stock
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	50	54
BBB+ to BBB- | CRA investments
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0	0
BB+ and below
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	0	0
Fair value	83	85
Investment securities - equity	29	35
BB+ and below | U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
BB+ and below | Residential MBS issued by GSEs and GNMA
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
BB+ and below | CLO
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
BB+ and below | Private label residential MBS
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	0	0
Fair value	0	1
BB+ and below | Tax-exempt
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	0	0
Fair value	0	0
BB+ and below | Commercial MBS issued by GSEs and GNMA
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
BB+ and below | Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Fair value	82	80
BB+ and below | Other
Debt Securities, Available-for-sale [Line Items]
Fair value	1	4
BB+ and below | Preferred Stock
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	29	35
BB+ and below | CRA investments
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	0	0
Unrated
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	1,526	1,429
Fair value	111	103
Investment securities - equity	12	11
Unrated | U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
Unrated | Residential MBS issued by GSEs and GNMA
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
Unrated | CLO
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
Unrated | Private label residential MBS
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	176	186
Fair value	0	0
Unrated | Tax-exempt
Debt Securities, Available-for-sale [Line Items]
Investment securities - amortized cost	1,350	1,243
Fair value	94	86
Unrated | Commercial MBS issued by GSEs and GNMA
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
Unrated | Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Fair value	0	0
Unrated | Other
Debt Securities, Available-for-sale [Line Items]
Fair value	17	17
Unrated | Preferred Stock
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	12	11
Unrated | CRA investments
Debt Securities, Available-for-sale [Line Items]
Investment securities - equity	$ 0	$ 0