VARIABLE INTEREST ENTITIES - Schedule of Affordable Housing Tax Credit Investments (Details) - LIHTC Investments - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Tax credits included in income tax expense	$ 101	$ 83	$ 59
Amortization expense included in income tax expense	110	94	59
Other tax benefits included in income tax expense	$ 25	$ 31	$ 21