RECLASSIFICATIONS OUT OF ACCUMULATED OTHER COMPREHENSIVE LOSS - Effects to Net Income of Amounts Reclassified Out of OCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net interest income	$ 4,173	$ 3,758	$ 3,402
Provision for credit losses	321	369	302
Noninterest income	1,534	1,497	1,422
Noninterest expense	3,474	3,352	3,259
Income before income tax expense	1,912	1,534	1,263
Income tax expense	260	489	423
NET INCOME	1,652	1,045	840
Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net interest income	25	63	23
Noninterest income	4	(1)	22
Noninterest expense	48	(39)	8
Income tax expense	(6)	38	17
NET INCOME	$ (13)	$ 63	$ 20