SECURITIES - Narrative (Details) - USD ($)	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Accrued interest receivable on debt securities	$ 54,000,000		$ 54,000,000		$ 55,000,000
Taxable interest income from securities	124,000,000	$ 130,000,000	252,000,000	$ 277,000,000
Offsetting of short-term receivables or payables recognized	$ 0		$ 0		$ 0
Held-to-maturity, zero expected credit loss, percent of portfolio	70.00%		70.00%
Held-to-maturity, expected credit loss, percent of portfolio	30.00%		30.00%
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Securitizations of mortgage loans	$ 82,000,000	$ 0	$ 163,000,000	$ 0

Debt Securities, Held To Maturity, Expected Credit Loss, Percent Of Portfolio

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- Definition

Debt Securities, Held To Maturity, Zero Expected Credit Loss, Percent Of Portfolio

+ References

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- Definition

Debt Securities, Interest Receivable

+ References

No definition available.

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- Definition

Amount of operating interest income, including amortization and accretion of premiums and discounts, on securities subject to state, federal and other income tax.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.2)
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

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- Definition

The cash inflow from securitizing loans held with the intention to resell in the near future.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 21
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3461-108585

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-Topic 230
-SubTopic 10
-Section 45
-Paragraph 16
-Subparagraph (a)
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount, before effects of master netting arrangements, of securities loaned to entities in exchange for collateral and funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price. Includes liabilities not subject to a master netting arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
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-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 7
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=109249958&loc=SL34722452-111729

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