INVESTMENT SECURITIES AND OTHER SECURITIES - Schedule of Amortized Cost, Fair Value, and Gross Unrealized Gains (Losses) (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Available-for-sale securities:
Total available-for-sale securities	$ 28,510	$ 30,743
Available-for-sale securities, Gross Gains	66	13
Available-for-sale securities, Gross Losses	(2,444)	(3,483)
Available-for-sale securities	26,132	27,273
Held-to-maturity securities:
Held to maturity securities	15,258	16,368
Held-to-maturity securities, Gross Gains	25	3
Held-to-maturity securities, Gross Losses	(1,647)	(2,285)
Held-to-maturity securities, Fair Value	13,636	14,086
Other securities, at cost:
Other securities, Amortized Cost	994	822
Other securities, Gross Gains	0	1
Other securities, Gross Losses	0	0
Other securities, Fair Value	$ 994	823
Debt Securities, Available-for-Sale, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration]	Accrued income and other receivables
Debt Securities, Held-to-Maturity, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration]	Accrued income and other receivables
Accrued interest receivable on AFS securities	$ 106	89
Accrued interest receivable on HTM securities	44	46
Cumulative basis adjustments associated with hedging relationships	177	458
U.S. Treasury
Available-for-sale securities:
Total available-for-sale securities	4,590	6,588
Available-for-sale securities, Gross Gains	45	11
Available-for-sale securities, Gross Losses	0	(43)
Available-for-sale securities	4,635	6,556
Held-to-maturity securities:
Held to maturity securities	2,349	2,045
Held-to-maturity securities, Gross Gains	19	0
Held-to-maturity securities, Gross Losses	0	(22)
Held-to-maturity securities, Fair Value	2,368	2,023
US Treasury and Government
Available-for-sale securities:
Total available-for-sale securities	23,758	25,008
Available-for-sale securities, Gross Gains	57	12
Available-for-sale securities, Gross Losses	(2,333)	(3,220)
Available-for-sale securities	21,482	21,800
Held-to-maturity securities:
Held to maturity securities	15,257	16,367
Held-to-maturity securities, Gross Gains	25	3
Held-to-maturity securities, Gross Losses	(1,647)	(2,285)
Held-to-maturity securities, Fair Value	13,635	14,085
Residential MBS
Available-for-sale securities:
Total available-for-sale securities	11,031	11,988
Available-for-sale securities, Gross Gains	3	0
Available-for-sale securities, Gross Losses	(1,365)	(1,971)
Available-for-sale securities	9,669	10,017
Held-to-maturity securities:
Held to maturity securities	7,718	8,533
Held-to-maturity securities, Gross Gains	1	0
Held-to-maturity securities, Gross Losses	(941)	(1,336)
Held-to-maturity securities, Fair Value	6,778	7,197
Residential CMO
Available-for-sale securities:
Total available-for-sale securities	5,496	3,778
Available-for-sale securities, Gross Gains	9	1
Available-for-sale securities, Gross Losses	(308)	(434)
Available-for-sale securities	5,197	3,345
Held-to-maturity securities:
Held to maturity securities	3,865	4,309
Held-to-maturity securities, Gross Gains	5	3
Held-to-maturity securities, Gross Losses	(520)	(691)
Held-to-maturity securities, Fair Value	3,350	3,621
Commercial MBS
Available-for-sale securities:
Total available-for-sale securities	2,488	2,519
Available-for-sale securities, Gross Gains	0	0
Available-for-sale securities, Gross Losses	(657)	(767)
Available-for-sale securities	1,831	1,752
Held-to-maturity securities:
Held to maturity securities	1,278	1,407
Held-to-maturity securities, Gross Gains	0	0
Held-to-maturity securities, Gross Losses	(184)	(231)
Held-to-maturity securities, Fair Value	1,094	1,176
Other agencies
Available-for-sale securities:
Total available-for-sale securities	153	135
Available-for-sale securities, Gross Gains	0	0
Available-for-sale securities, Gross Losses	(3)	(5)
Available-for-sale securities	150	130
Held-to-maturity securities:
Held to maturity securities	47	73
Held-to-maturity securities, Gross Gains	0	0
Held-to-maturity securities, Gross Losses	(2)	(5)
Held-to-maturity securities, Fair Value	45	68
Municipal securities
Available-for-sale securities:
Total available-for-sale securities	4,215	4,119
Available-for-sale securities, Gross Gains	9	1
Available-for-sale securities, Gross Losses	(81)	(132)
Available-for-sale securities	4,143	3,988
Held-to-maturity securities:
Held to maturity securities	1	1
Held-to-maturity securities, Gross Gains	0	0
Held-to-maturity securities, Gross Losses	0	0
Held-to-maturity securities, Fair Value	1	1
Corporate debt
Available-for-sale securities:
Total available-for-sale securities	193	1,157
Available-for-sale securities, Gross Gains	0	0
Available-for-sale securities, Gross Losses	(15)	(102)
Available-for-sale securities	178	1,055
Asset-backed securities
Available-for-sale securities:
Total available-for-sale securities	229	330
Available-for-sale securities, Gross Gains	0	0
Available-for-sale securities, Gross Losses	(8)	(19)
Available-for-sale securities	221	311
Private-label CMO
Available-for-sale securities:
Total available-for-sale securities	105	119
Available-for-sale securities, Gross Gains	0	0
Available-for-sale securities, Gross Losses	(7)	(10)
Available-for-sale securities	98	109
Other securities/sovereign debt
Available-for-sale securities:
Total available-for-sale securities	10	10
Available-for-sale securities, Gross Gains	0	0
Available-for-sale securities, Gross Losses	0	0
Available-for-sale securities	10	10
Non-marketable equity securities: | FRB stock
Other securities, at cost:
Other securities, Amortized Cost	616	521
Other securities, Gross Gains	0	0
Other securities, Gross Losses	0	0
Other securities, Fair Value	616	521
Non-marketable equity securities: | FHLB stock
Other securities, at cost:
Other securities, Amortized Cost	288	246
Other securities, Gross Gains	0	0
Other securities, Gross Losses	0	0
Other securities, Fair Value	288	246
Other non-marketable equity securities
Other securities, at cost:
Other securities, Amortized Cost	48	25
Other securities, Gross Gains	0	0
Other securities, Gross Losses	0	0
Other securities, Fair Value	48	25
Mutual funds
Other securities, at cost:
Other securities, Amortized Cost	30	29
Other securities, Gross Gains	0	0
Other securities, Gross Losses	0	0
Other securities, Fair Value	30	29
Equity securities
Other securities, at cost:
Other securities, Amortized Cost	12	1
Other securities, Gross Gains	0	1
Other securities, Gross Losses	0	0
Other securities, Fair Value	$ 12	$ 2