FAIR VALUE MEASUREMENTS - Residential Mortgage and Commercial Real Estate Loans Held For Sale (Details) - Level 2 - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Mortgage banking fees \| Residential loans held for sale
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Changes in fair value	$ (4)	$ (8)	$ 5	$ (7)
Other income \| Commercial and commercial real estate loans held for sale, at fair value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Changes in fair value	$ 0	$ 1	$ 4	$ 1

For each line item in the statement of financial position, the amounts of gains and losses from fair value changes included in earnings.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14172-108612

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