INVESTMENT SECURITIES - Schedule of Amortized Cost and Fair Value of Securities Available for Sale (Details) - USD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 3,927	$ 3,783
Gross Unrealized Gains	1	29
Gross Unrealized Losses	(181)	(85)
Fair Value	3,747	3,727
U.S. Treasury
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	403	354
Gross Unrealized Gains	0	2
Gross Unrealized Losses	(6)	0
Fair Value	397	356
U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	27	35
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	27	35
U.S. GSE
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	290	266
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(10)	0
Fair Value	280	266
Agency MBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	746	801
Gross Unrealized Gains	0	7
Gross Unrealized Losses	(36)	(8)
Fair Value	710	800
Agency CMO
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	570	662
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(76)	(61)
Fair Value	494	601
Agency commercial MBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,799	1,595
Gross Unrealized Gains	1	19
Gross Unrealized Losses	(50)	(15)
Fair Value	1,750	1,599
States of the U.S. and political subdivisions (municipals)
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	11	20
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	(1)
Fair Value	10	19
Other debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	81	50
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(2)	0
Fair Value	$ 79	$ 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 excluding accrued interest, of 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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