SECURITIES - Amortized Cost and Fair Value of Securities Available for Sale (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 3,600	$ 3,416
Gross Unrealized Gains	2	36
Gross Unrealized Losses	(156)	(26)
Debt securities, available for sale	3,446	3,426
U.S. Treasury
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	205	205
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(11)	(1)
Debt securities, available for sale	194	204
U.S. government agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	140	154
Gross Unrealized Gains	1	1
Gross Unrealized Losses	0	0
Debt securities, available for sale	141	155
U.S. government-sponsored entities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	214	194
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(10)	(2)
Debt securities, available for sale	204	192
Agency mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,440	1,342
Gross Unrealized Gains	1	19
Gross Unrealized Losses	(54)	(4)
Debt securities, available for sale	1,387	1,357
Agency collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,236	1,192
Gross Unrealized Gains	0	11
Gross Unrealized Losses	(67)	(17)
Debt securities, available for sale	1,169	1,186
Commercial mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	320	294
Gross Unrealized Gains	0	5
Gross Unrealized Losses	(12)	(2)
Debt securities, available for sale	308	297
States of the U.S. and political subdivisions (municipals)
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	33	33
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2)	0
Debt securities, available for sale	31	33
Other debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	12	2
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Debt securities, available for sale	$ 12	$ 2

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

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- Definition

Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

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- Definition

Amortized cost excluding accrued interest, before allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

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Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
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-Topic 326
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