ALLOWANCE FOR CREDIT LOSSES, NONACCRUAL LOANS AND LEASES, AND CONCENTRATIONS OF CREDIT RISK - Schedule of Additional Detail on the Cumulative Effect of Change in Accounting Principle (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 128,163	$ 123,090
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	60,350	60,793
Commercial | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	44,500	44,173
Commercial | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	14,264	14,652
Commercial | Leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	1,586	1,968
Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	67,813	62,297
Retail | Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	22,822	19,539
Retail | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	12,015	12,149
Retail | Automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	14,549	12,153
Retail | Education
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	12,997	12,308
Retail | Other retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 5,430	$ 6,148