COMMITMENTS AND CONTINGENCIES - Schedule of Outstanding Off-balance sheet Arrangements (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Other Commitments [Line Items]
Commitment amount	$ 67,077	$ 75,040
Commitments to extend credit
Other Commitments [Line Items]
Commitment amount	64,827	72,743
Letters of credit
Other Commitments [Line Items]
Commitment amount	2,064	2,190
Risk participation agreements
Other Commitments [Line Items]
Commitment amount	106	37
Loans sold with recourse
Other Commitments [Line Items]
Commitment amount	49	37
Marketing rights
Other Commitments [Line Items]
Commitment amount	$ 31	$ 33