COMMITMENTS AND CONTINGENCIES - Schedule of Outstanding Off-balance sheet Arrangements (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Other Commitments [Line Items]
Commitment amount	$ 70,739	$ 71,739
Commitments to extend credit
Other Commitments [Line Items]
Commitment amount	68,564	69,553
Letters of credit
Other Commitments [Line Items]
Commitment amount	2,089	2,125
Marketing rights
Other Commitments [Line Items]
Commitment amount	37	37
Risk participation agreements
Other Commitments [Line Items]
Commitment amount	27	19
Loans sold with recourse
Other Commitments [Line Items]
Commitment amount	$ 22	$ 5