ALLOWANCE FOR CREDIT LOSSES, NONPERFORMING ASSETS, AND CONCENTRATIONS OF CREDIT RISK - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	$ 326	$ 321		$ 369
Minimum qualifying balance	3
Nonperforming assets, net of valuation allowance	34	36
Mortgage loans collateralized by OREO	$ 172	181
High loan to value criteria (exceeds)	90.00%
Allowance for loan and lease losses
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for credit losses	$ 323	$ 305	[1]	$ 355

[1] Includes an increase of approximately $50 million to commercial and corresponding decrease to retail for the impact of the enhancement to the assessment of qualitative risks, factors and events that may not be measured in the modeled results.