LOANS AND LEASES - Net of Unearned Income (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost loans and leases, carrying amount	$ 26,839	$ 24,968
Total commercial loans and leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost loans and leases, carrying amount	17,581	16,465
Total commercial loans and leases | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost loans and leases, carrying amount	10,746	9,899
Total commercial loans and leases | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost loans and leases, carrying amount	6,220	5,977
Total commercial loans and leases | Commercial leases
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost loans and leases, carrying amount	471	495
Total commercial loans and leases | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost loans and leases, carrying amount	144	94
Total consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost loans and leases, carrying amount	9,258	8,503
Total consumer loans | Direct installment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost loans and leases, carrying amount	2,568	2,376
Total consumer loans | Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost loans and leases, carrying amount	4,188	3,654
Total consumer loans | Indirect installment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost loans and leases, carrying amount	1,216	1,227
Total consumer loans | Consumer lines of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost loans and leases, carrying amount	$ 1,286	$ 1,246