VARIABLE INTEREST ENTITIES - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Variable Interest Entity [Line Items]
Lending to special purpose entities included in loans and leases	$ 128,163,000,000	$ 123,090,000,000
Purchases of debt securities available for sale	12,406,000,000	9,271,000,000	$ 8,422,000,000
LIHTC Investments
Variable Interest Entity [Line Items]
Net impairment losses recognized in earnings	0	0	$ 0
Commitments to extend credit | Special Purpose Entities
Variable Interest Entity [Line Items]
Undrawn commitments to extend credit	1,900,000,000	1,500,000,000
Commercial and industrial | Special Purpose Entities
Variable Interest Entity [Line Items]
Lending to special purpose entities included in loans and leases	2,646,000,000	1,295,000,000
Retail
Variable Interest Entity [Line Items]
Lending to special purpose entities included in loans and leases	67,813,000,000	62,297,000,000
Retail | Education
Variable Interest Entity [Line Items]
Lending to special purpose entities included in loans and leases	$ 12,997,000,000	$ 12,308,000,000