LOANS AND LEASES - Summary of Loans and Leases Portfolio (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 119,088	$ 116,660
Loans held for sale	3,300	1,300
Mortgage loans serviced for others | Banking Subsidiaries
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	77,500	69,600
SBA Loans Serviced For Others | Banking Subsidiaries
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	33	0
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	57,538	56,783
Commercial | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	41,479	40,857
Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	13,522	13,023
Commercial | Leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	2,537	2,903
Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	61,550	59,877
Retail | Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	19,083	18,978
Retail | Home equity loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	812	1,073
Retail | Home equity lines of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	11,979	12,710
Retail | Home equity loans serviced by others
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	289	399
Retail | Home equity lines of credit serviced by others
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	74	104
Retail | Automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	12,120	12,106
Retail | Education
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	10,347	8,900
Retail | Credit cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	2,198	1,991
Retail | Other retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 4,648	$ 3,616