SECURITIES - Amortized Cost and Fair Value of Securities Held to Maturity (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Investment Securities Held To Maturity [Line Items]
Amortized Cost	$ 3,922	$ 4,087
Gross Unrealized Gains	0	3
Gross Unrealized Losses	(519)	(403)
Fair Value	3,403	3,687
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	93	52
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	0
Fair Value	92	52
Agency mortgage-backed securities
Investment Securities Held To Maturity [Line Items]
Amortized Cost	1,052	1,178
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(144)	(125)
Fair Value	908	1,053
Agency collateralized mortgage obligations
Investment Securities Held To Maturity [Line Items]
Amortized Cost	852	953
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(132)	(120)
Fair Value	720	833
Commercial mortgage-backed securities
Investment Securities Held To Maturity [Line Items]
Amortized Cost	891	866
Gross Unrealized Gains	0	2
Gross Unrealized Losses	(68)	(50)
Fair Value	823	818
States of the U.S. and political subdivisions (municipals)
Investment Securities Held To Maturity [Line Items]
Amortized Cost	1,017	1,025
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(172)	(107)
Fair Value	845	919
Other debt securities
Investment Securities Held To Maturity [Line Items]
Amortized Cost	16	12
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2)	(1)
Fair Value	$ 14	$ 11

Investment Securities Held To Maturity [Line Items]

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- Definition

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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- Definition

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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