ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Default of Modified Debt Agreements (Details) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018 USD ($) contract	Jun. 30, 2017 USD ($) contract	Jun. 30, 2018 USD ($) contract	Jun. 30, 2017 USD ($) contract
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	239	272	521	536
Balance Defaulted \| $	$ 27	$ 12	$ 40	$ 26
Commercial
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	4	4	7	6
Balance Defaulted \| $	$ 17	$ 1	$ 20	$ 5
Commercial \| Commercial
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	3	4	6	5
Balance Defaulted \| $	$ 17	$ 1	$ 20	$ 1
Commercial \| Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	1	0	1	1
Balance Defaulted \| $	$ 0	$ 0	$ 0	$ 4
Commercial \| Leases
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	0	0	0	0
Balance Defaulted \| $	$ 0	$ 0	$ 0	$ 0
Retail
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	235	268	514	530
Balance Defaulted \| $	$ 10	$ 11	$ 20	$ 21
Retail \| Residential mortgages
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	44	41	70	86
Balance Defaulted \| $	$ 5	$ 4	$ 8	$ 10
Retail \| Home equity loans
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	7	14	18	23
Balance Defaulted \| $	$ 0	$ 1	$ 1	$ 1
Retail \| Home equity lines of credit
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	40	65	106	100
Balance Defaulted \| $	$ 3	$ 4	$ 8	$ 7
Retail \| Home equity loans serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	5	9	10	10
Balance Defaulted \| $	$ 0	$ 0	$ 0	$ 0
Retail \| Home equity lines of credit serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	0	1	1	4
Balance Defaulted \| $	$ 0	$ 0	$ 0	$ 0
Retail \| Automobile
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	30	27	76	61
Balance Defaulted \| $	$ 1	$ 1	$ 1	$ 1
Retail \| Education
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	7	9	12	16
Balance Defaulted \| $	$ 1	$ 0	$ 1	$ 0
Retail \| Credit cards
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	102	102	221	228
Balance Defaulted \| $	$ 0	$ 1	$ 1	$ 2
Retail \| Other retail
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	0	0	0	2
Balance Defaulted \| $	$ 0	$ 0	$ 0	$ 0

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- Definition

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953682-111524

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Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

+ References

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