ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Nonaccrual Loans and Leases by Class (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Nonaccrual loans and leases	$ 780	$ 703
90 days past due and accruing	27
Nonaccrual with no related ACL	232
Residential mortgages
Financing Receivable, Past Due [Line Items]
90 days past due and accruing		0
Commercial
Financing Receivable, Past Due [Line Items]
Nonaccrual loans and leases	314	245
90 days past due and accruing	0
Nonaccrual with no related ACL	52
Commercial \| Commercial
Financing Receivable, Past Due [Line Items]
Nonaccrual loans and leases	305	240
90 days past due and accruing	0
Nonaccrual with no related ACL	46
Commercial \| Commercial real estate
Financing Receivable, Past Due [Line Items]
Nonaccrual loans and leases	8	2
90 days past due and accruing	0
Nonaccrual with no related ACL	6
Commercial \| Leases
Financing Receivable, Past Due [Line Items]
Nonaccrual loans and leases	1	3
90 days past due and accruing	0
Nonaccrual with no related ACL	0
Retail
Financing Receivable, Past Due [Line Items]
Nonaccrual loans and leases	466	458
90 days past due and accruing	27
Nonaccrual with no related ACL	180
Retail \| Residential mortgages
Financing Receivable, Past Due [Line Items]
Nonaccrual loans and leases	101	93
90 days past due and accruing	14
Nonaccrual with no related ACL	55
Retail \| Home equity
Financing Receivable, Past Due [Line Items]
Nonaccrual loans and leases	242	246
90 days past due and accruing	0
Nonaccrual with no related ACL	90
Retail \| Automobile
Financing Receivable, Past Due [Line Items]
Nonaccrual loans and leases	69	67
90 days past due and accruing	0
Nonaccrual with no related ACL	30
Retail \| Education
Financing Receivable, Past Due [Line Items]
Nonaccrual loans and leases	21	18
90 days past due and accruing	2
Nonaccrual with no related ACL	4
Retail \| Other retail
Financing Receivable, Past Due [Line Items]
Nonaccrual loans and leases	33	$ 34
90 days past due and accruing	11
Nonaccrual with no related ACL	$ 1

Amount of financing receivable on nonaccrual status with no allowance for credit loss.

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Balance Type:	debit
Period Type:	instant

- Definition

Amount of financing receivable 90 days or more past due and still accruing.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 16
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919258-210447

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
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Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
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-Section 55
-Paragraph 80
-URI http://asc.fasb.org/extlink&oid=118955255&loc=SL82922355-210448

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Definition

Amount of financing receivable on nonaccrual status.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
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-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5111-111524

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 16
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919258-210447

+ 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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