LOANS AND LEASES - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income on direct financing and sales-type leases	$ 77
Retail \| Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged as collateral for FHLB borrowed funds	25,300	$ 25,600
Retail \| Education loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchases	1,100	457
Retail \| Other loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchases	530
Retail \| Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Sales	628
Retail \| Retail ,TDRs
Accounts, Notes, Loans and Financing Receivable [Line Items]
Sales	22
Commercial \| Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Sales	454	553
Retail and Commercial \| Auto, commercial and commercial real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged as collateral to support the contingent ability to borrow at the FRB discount window	$ 17,400	$ 16,800
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term of contract	3 years
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term of contract	7 years

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Amount of interest income from net investment in direct financing lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 270
-SubTopic 10
-Section 50
-Paragraph 6A
-URI http://asc.fasb.org/extlink&oid=118952077&loc=SL77927221-108306

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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The cash outflow for the purchase of amounts due from customers, clients, lessees, borrowers, or others under the terms of its agreements therewith.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
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+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
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The carrying amount, as of the date of the latest financial statement presented, of loans receivable which are owned but transferred to serve as collateral for the payment of other debt obligations, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

+ References

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The cash inflow associated with the sale of receivables arising from the financing of goods and services.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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-Section 45
-Paragraph 12
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