INVESTMENT SECURITIES - Schedule of Amortized Cost and Fair Value of Securities Available for Sale (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 3,588	$ 3,620
Gross Unrealized Gains	14	4
Gross Unrealized Losses	(125)	(158)
Fair  Value	3,477	3,466
U.S. Treasury
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	274	274
Gross Unrealized Gains	1	1
Gross Unrealized Losses	0	(1)
Fair  Value	275	274
U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	50	53
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair  Value	50	53
U.S. government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	303	302
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	(2)
Fair  Value	302	300
Agency MBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	709	714
Gross Unrealized Gains	3	0
Gross Unrealized Losses	(14)	(20)
Fair  Value	698	694
Agency collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	761	796
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(83)	(98)
Fair  Value	678	698
Agency commercial MBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,430	1,420
Gross Unrealized Gains	10	3
Gross Unrealized Losses	(25)	(35)
Fair  Value	1,415	1,388
States of the U.S. and political subdivisions (municipals)
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	21	24
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2)	(2)
Fair  Value	19	22
Other debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	40	37
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair  Value	$ 40	$ 37