RECLASSIFICATIONS OUT OF ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Effects to Net Income of Amounts Reclassified Out of OCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net interest income	$ 4,532	$ 4,173	$ 3,758
Provision for credit losses	326	321	369
Noninterest income	1,596	1,534	1,497
Noninterest expense	3,619	3,474	3,352
Income before income tax expense	2,183	1,912	1,534
Income tax expense	462	260	489
NET INCOME	1,721	1,652	1,045
Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net interest income	(43)	25	63
Noninterest income	16	4	(1)
Noninterest expense	(33)	48	(39)
Income tax expense	5	(6)	38
NET INCOME	$ 1	$ (13)	$ 63