SECURITIES - Schedule of Amortized Cost and Fair Value of Securities Held to Maturity (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Investment Securities Held To Maturity [Line Items]
Amortized Cost	$ 3,893	$ 3,911
Gross Unrealized Gains	4	8
Gross Unrealized Losses	(350)	(326)
Fair Value	3,547	3,593
U.S. Treasury
Investment Securities Held To Maturity [Line Items]
Amortized Cost	1
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	1
U.S. government agencies
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. government-sponsored entities
Investment Securities Held To Maturity [Line Items]
Amortized Cost	28	68
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	28	68
Agency MBS
Investment Securities Held To Maturity [Line Items]
Amortized Cost	1,018	1,057
Gross Unrealized Gains	1	2
Gross Unrealized Losses	(105)	(101)
Fair Value	914	958
Agency collateralized mortgage obligations
Investment Securities Held To Maturity [Line Items]
Amortized Cost	797	824
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(108)	(104)
Fair Value	689	720
Agency commercial MBS
Investment Securities Held To Maturity [Line Items]
Amortized Cost	1,023	929
Gross Unrealized Gains	2	4
Gross Unrealized Losses	(51)	(43)
Fair Value	974	890
States of the U.S. and political subdivisions (municipals)
Investment Securities Held To Maturity [Line Items]
Amortized Cost	1,009	1,017
Gross Unrealized Gains	1	2
Gross Unrealized Losses	(85)	(77)
Fair Value	925	942
Other debt securities
Investment Securities Held To Maturity [Line Items]
Amortized Cost	16	15
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	(1)
Fair Value	$ 15	$ 14

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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).

+ References

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-Topic 326
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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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Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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