MORTGAGE BANKING - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 124,071	$ 119,088
Mortgage loans serviced for others \| Banking Subsidiaries
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 80,700	$ 77,500

Amount, before allowance for credit loss, of financing receivable.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 79
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
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-Section 50
-Paragraph 5
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Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
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