SECURITIES - Amortized Cost and Fair Value of Securities Held to Maturity (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Investment Securities Held To Maturity [Line Items]
Amortized Cost	$ 3,513	$ 3,463
Gross Unrealized Gains	5	62
Gross Unrealized Losses	(154)	(19)
Fair Value	3,364	3,506
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. 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
Agency mortgage-backed securities
Investment Securities Held To Maturity [Line Items]
Amortized Cost	1,261	1,191
Gross Unrealized Gains	1	15
Gross Unrealized Losses	(53)	(5)
Fair Value	1,209	1,201
Agency collateralized mortgage obligations
Investment Securities Held To Maturity [Line Items]
Amortized Cost	943	930
Gross Unrealized Gains	0	5
Gross Unrealized Losses	(55)	(12)
Fair Value	888	923
Commercial mortgage-backed securities
Investment Securities Held To Maturity [Line Items]
Amortized Cost	328	323
Gross Unrealized Gains	0	3
Gross Unrealized Losses	(16)	(2)
Fair Value	312	324
States of the U.S. and political subdivisions (municipals)
Investment Securities Held To Maturity [Line Items]
Amortized Cost	974	1,017
Gross Unrealized Gains	4	39
Gross Unrealized Losses	(30)	0
Fair Value	948	$ 1,056
Other debt securities
Investment Securities Held To Maturity [Line Items]
Amortized Cost	5
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	$ 5

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)
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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).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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