SECURITIES - Amortized Cost and Fair Value of Securities Held to Maturity (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Investment Securities Held To Maturity [Line Items]
Amortized Cost	$ 4,073	$ 4,087
Gross Unrealized Gains	7	3
Gross Unrealized Losses	(338)	(403)
Fair Value	3,742	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	92	52
Gross Unrealized Gains	1	0
Gross Unrealized Losses	0	0
Fair Value	93	52
Agency mortgage-backed securities
Investment Securities Held To Maturity [Line Items]
Amortized Cost	1,139	1,178
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(110)	(125)
Fair Value	1,029	1,053
Agency collateralized mortgage obligations
Investment Securities Held To Maturity [Line Items]
Amortized Cost	920	953
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(107)	(120)
Fair Value	813	833
Commercial mortgage-backed securities
Investment Securities Held To Maturity [Line Items]
Amortized Cost	873	866
Gross Unrealized Gains	3	2
Gross Unrealized Losses	(44)	(50)
Fair Value	832	818
States of the U.S. and political subdivisions (municipals)
Investment Securities Held To Maturity [Line Items]
Amortized Cost	1,032	1,025
Gross Unrealized Gains	3	1
Gross Unrealized Losses	(76)	(107)
Fair Value	959	919
Other debt securities
Investment Securities Held To Maturity [Line Items]
Amortized Cost	16	12
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	(1)
Fair Value	$ 15	$ 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).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919230-210447

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 3B
-URI https://asc.fasb.org/extlink&oid=124255953&loc=SL120267963-210447

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
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-URI https://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446

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- Definition

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

+ References

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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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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27232-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
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-URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878

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