DERIVATIVES - Effect of Customer Derivatives and Economic Hedges on Net Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Amounts Recognized in Noninterest Income	$ 57	$ 15	$ 100	$ 47
Economic hedges | Foreign exchange and interest rate products | Customer interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amounts Recognized in Noninterest Income	(84)	12	(363)	92
Economic hedges | Foreign exchange and interest rate products | Customer foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amounts Recognized in Noninterest Income	30	61	(27)	157
Economic hedges | Foreign exchange and interest rate products | Derivatives transactions to hedge interest rate risk
Derivative Instruments, Gain (Loss) [Line Items]
Amounts Recognized in Noninterest Income	97	(2)	403	(58)
Economic hedges | Foreign exchange and interest rate products | Derivatives transactions to hedge foreign exchange risk
Derivative Instruments, Gain (Loss) [Line Items]
Amounts Recognized in Noninterest Income	24	(55)	99	(140)
Economic hedges | Mortgage banking fees | Residential loan commitments
Derivative Instruments, Gain (Loss) [Line Items]
Amounts Recognized in Noninterest Income	6	0	6	3
Economic hedges | Mortgage banking fees | Forward sale contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amounts Recognized in Noninterest Income	(13)	(1)	(15)	(7)
Economic hedges | Mortgage banking fees | Interest rate derivative contracts used to hedge residential MSRs
Derivative Instruments, Gain (Loss) [Line Items]
Amounts Recognized in Noninterest Income	$ (3)	$ 0	$ (3)	$ 0