LOANS AND LEASES - Summary of Loans and Leases Portfolio (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 117,880	$ 116,660
Loans receivable held for sale	2,000	1,300
SBA Loans Serviced For Others | Banking and Other Subsidiaries
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	27	0
Mortgage loans serviced for others | Banking and Other Subsidiaries
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	74,600	69,600
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	56,733	56,783
Commercial | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	41,356	40,857
Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	12,820	13,023
Commercial | Leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	2,557	2,903
Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	61,147	59,877
Retail | Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	19,699	18,978
Retail | Home equity loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	876	1,073
Retail | Home equity lines of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	12,148	12,710
Retail | Home equity loans serviced by others
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	318	399
Retail | Home equity lines of credit serviced by others
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	81	104
Retail | Automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	12,070	12,106
Retail | Education
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	9,729	8,900
Retail | Credit cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	2,133	1,991
Retail | Other retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 4,093	$ 3,616