ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Financing Receivable, Modifications [Line Items]
Nonperforming assets, net of valuation allowance	$ 32		$ 32		$ 34
Mortgage loans collateralized by OREO	174		174		$ 172
Larger balance commercial loans minimum balance (greater than)	3		3
Net change to ALLL from modification	2	$ 1	4	$ 2
Charge-offs from modification of loans	1	1	$ 2	2
High loan to value criteria (exceeds)			90.00%
Commercial \| Commercial
Financing Receivable, Modifications [Line Items]
TDR's that defaulted within 12 months of modification date	1	17	$ 1	20
Retail \| Retail
Financing Receivable, Modifications [Line Items]
TDR's that defaulted within 12 months of modification date	$ 10	$ 10	$ 19	$ 19

Minimum qualifying carrying balance of commercial loans.

No definition available.

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- Definition

An entity's internal risk assessment as having high risk defined as certain loans with outstanding balances exceeding a percentage of the value of underlying collateral.

+ References

No definition available.

+ Details

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- Definition

Recorded investment in non performing assets receivable net of valuation allowance as of the balance sheet date.

+ References

No definition available.

+ Details

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- Definition

Recorded investment in financing receivables that are on nonaccrual status and are collateralized by land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement as of the balance sheet date.

+ References

No definition available.

+ Details

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- Definition

The effect of a change in method or methods for calculating the allowance for credit losses on the current period provision.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

+ Details

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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.

+ Details

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- Definition

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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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- Definition

Reflects the amount of the write-down related to a troubled debt restructuring.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=82895541&loc=d3e18845-111554

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