LOANS AND LEASES - Summary of Loans and Leases Portfolio (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 117,615	$ 116,660
Loans receivable held for sale	1,300	1,300
SBA Loans Serviced For Others | Banking and Other Subsidiaries
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	17	0
Mortgage loans serviced for others | Banking and Other Subsidiaries
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	70,800	69,600
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	57,689	56,783
Commercial | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	41,497	40,857
Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	13,372	13,023
Commercial | Leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	2,820	2,903
Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	59,926	59,877
Retail | Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	19,174	18,978
Retail | Home equity loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	1,006	1,073
Retail | Home equity lines of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	12,394	12,710
Retail | Home equity loans serviced by others
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	375	399
Retail | Home equity lines of credit serviced by others
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	95	104
Retail | Automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	11,992	12,106
Retail | Education
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	9,274	8,900
Retail | Credit cards
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	1,982	1,991
Retail | Other retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 3,634	$ 3,616