RECLASSIFICATIONS OUT OF ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Effects to Net Income of Amounts Reclassified Out of OCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net interest income	$ 1,148	$ 1,062	$ 3,360	$ 3,093
Provision for credit losses	78	72	241	238
Noninterest income	416	381	1,175	1,130
Noninterest expense	910	858	2,668	2,576
Income before income tax expense	576	513	1,626	1,409
Income tax expense	133	165	370	423
NET INCOME	443	348	1,256	986
Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net interest income	(14)	4	(25)	21
Noninterest income	2	1	10	3
Noninterest expense	5	5	13	14
Income tax expense	(4)	0	(7)	3
NET INCOME	$ (13)	$ 0	$ (21)	$ 7