COMMITMENTS AND CONTINGENCIES - Schedule of Outstanding Off-balance sheet Arrangements (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Other Commitments [Line Items]
Commitment amount	$ 75,485	$ 75,040
Commitments to extend credit
Other Commitments [Line Items]
Commitment amount	73,173	72,743
Letters of credit
Other Commitments [Line Items]
Commitment amount	2,132	2,190
Risk participation agreements
Other Commitments [Line Items]
Commitment amount	103	37
Loans sold with recourse
Other Commitments [Line Items]
Commitment amount	48	37
Marketing rights
Other Commitments [Line Items]
Commitment amount	$ 29	$ 33