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INVESTMENT SECURITIES - Schedule of Amortized Cost and Fair Value of Securities Held to Maturity (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Investment Securities Held To Maturity [Line Items]
Amortized Cost	$ 4,049	$ 3,979
Gross Unrealized Gains	19	3
Gross Unrealized Losses	(230)	(338)
Fair  Value	3,838	3,644
U.S. Treasury
Investment Securities Held To Maturity [Line Items]
Amortized Cost	1	1
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair  Value	1	1
U.S. GSE
Investment Securities Held To Maturity [Line Items]
Amortized Cost		29
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair  Value		29
Agency MBS
Investment Securities Held To Maturity [Line Items]
Amortized Cost	821	901
Gross Unrealized Gains	2	1
Gross Unrealized Losses	(62)	(96)
Fair  Value	761	806
Agency CMO
Investment Securities Held To Maturity [Line Items]
Amortized Cost	637	714
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(68)	(95)
Fair  Value	569	619
Agency commercial MBS
Investment Securities Held To Maturity [Line Items]
Amortized Cost	1,595	1,326
Gross Unrealized Gains	16	2
Gross Unrealized Losses	(22)	(44)
Fair  Value	1,589	1,284
States of the U.S. and political subdivisions (municipals)
Investment Securities Held To Maturity [Line Items]
Amortized Cost	984	992
Gross Unrealized Gains	1	0
Gross Unrealized Losses	(77)	(103)
Fair  Value	908	889
Other debt securities
Investment Securities Held To Maturity [Line Items]
Amortized Cost	11	16
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	0
Fair  Value	$ 10	$ 16

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Amount excluding accrued interest, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

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