LOANS AND LEASES - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest receivable	$ 449	$ 495
Interest income on direct financing and sales-type leases	64	77
Retail \| Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged as collateral for FHLB borrowed funds	25,500	25,300
Retail \| Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Sales	1,500
Retail \| Education loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchases	2,400	1,100
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
Retail \| Other Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchases	870	530
Commercial \| Education loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Sales	1,000
Commercial \| Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Sales	500	454
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	$ 40,000	$ 17,400
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	10 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
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-Publisher FASB
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-Section 50
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Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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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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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 FHLB debt obligations, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 30
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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.

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

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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