INVESTMENT SECURITIES - Schedule of Amortized Cost and Fair Value of Securities Available for Sale (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 3,854	$ 3,783
Gross Unrealized Gains	16	29
Gross Unrealized Losses	(95)	(85)
Fair Value	3,775	3,727
U.S. Treasury
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	354	354
Gross Unrealized Gains	1	2
Gross Unrealized Losses	(1)	0
Fair Value	354	356
U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	31	35
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	31	35
U.S. GSE
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	266	266
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	0
Fair Value	265	266
Agency MBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	824	801
Gross Unrealized Gains	4	7
Gross Unrealized Losses	(12)	(8)
Fair Value	816	800
Agency CMO
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	631	662
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(63)	(61)
Fair Value	568	601
Agency commercial MBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,659	1,595
Gross Unrealized Gains	11	19
Gross Unrealized Losses	(16)	(15)
Fair Value	1,654	1,599
States of the U.S. and political subdivisions (municipals)
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	13	20
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	(1)
Fair Value	12	19
Other debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	76	50
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(1)	0
Fair Value	$ 75	$ 51

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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