COMMITMENTS AND CONTINGENCIES - Schedule of Outstanding Off-balance sheet Arrangements (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Other Commitments [Line Items]
Commitment amount	$ 78,845	$ 76,580
Commitments to extend credit
Other Commitments [Line Items]
Commitment amount	76,761	74,160
Letters of credit
Other Commitments [Line Items]
Commitment amount	1,926	2,239
Risk participation agreements
Other Commitments [Line Items]
Commitment amount	68	98
Loans sold with recourse
Other Commitments [Line Items]
Commitment amount	64	54
Marketing rights
Other Commitments [Line Items]
Commitment amount	$ 26	$ 29