ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Default of Modified Debt Agreements (Details) $ in Millions	3 Months Ended
Mar. 31, 2018 USD ($) contract	Mar. 31, 2017 USD ($) contract
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	282	264
Balance Defaulted \| $	$ 13	$ 14
Commercial
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	3	2
Balance Defaulted \| $	$ 3	$ 4
Commercial \| Commercial
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	3	1
Balance Defaulted \| $	$ 3	$ 0
Commercial \| Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	0	1
Balance Defaulted \| $	$ 0	$ 4
Commercial \| Leases
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	0	0
Balance Defaulted \| $	$ 0	$ 0
Retail
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	279	262
Balance Defaulted \| $	$ 10	$ 10
Retail \| Residential mortgages
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	26	45
Balance Defaulted \| $	$ 3	$ 6
Retail \| Home equity loans
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	11	9
Balance Defaulted \| $	$ 1	$ 0
Retail \| Home equity lines of credit
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	66	35
Balance Defaulted \| $	$ 5	$ 3
Retail \| Home equity loans serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	5	1
Balance Defaulted \| $	$ 0	$ 0
Retail \| Home equity lines of credit serviced by others
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	1	3
Balance Defaulted \| $	$ 0	$ 0
Retail \| Automobile
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	46	34
Balance Defaulted \| $	$ 0	$ 0
Retail \| Education
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	5	7
Balance Defaulted \| $	$ 0	$ 0
Retail \| Credit cards
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	119	126
Balance Defaulted \| $	$ 1	$ 1
Retail \| Other retail
Financing Receivable, Modifications [Line Items]
Number of Contracts \| contract	0	2
Balance Defaulted \| $	$ 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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