FAIR VALUE MEASUREMENTS - Residential Mortgage and Commercial Real Estate Loans Held For Sale (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Aggregate Fair Value	$ 2,911	$ 1,946
Residential loans held for sale
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Aggregate Fair Value	2,708	1,778
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Aggregate Fair Value	2,911	1,946
Level 2 \| Residential loans held for sale
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Aggregate Fair Value	2,708	1,778
Aggregate Unpaid Principal	2,570	1,727
Aggregate Fair Value Less Aggregate Unpaid Principal	138	51
Level 2 \| Commercial and commercial real estate loans held for sale, at fair value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Aggregate Fair Value	203	168
Aggregate Unpaid Principal	232	175
Aggregate Fair Value Less Aggregate Unpaid Principal	$ (29)	$ (7)

The aggregate unpaid principal balance of loans measured at fair value.

No definition available.

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- Definition

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.

+ References

No definition available.

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- Definition

This item represents the difference between the aggregate fair value and the aggregate unpaid principal balance of loans and long-term receivables (other than securities categorized as trading, available-for-sale or held-to-maturity) that have contractual principal amounts and for which the fair value option has been elected.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (d)(1)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

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- Definition

The face amount of loans that will be sold to other entities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=118952595&loc=d3e4428-111522

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