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		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net interest income	$ 1,166	$ 1,121	$ 2,326	$ 2,212
Provision for credit losses	97	85	182	163
Noninterest income	462	388	890	759
Noninterest expense	951	875	1,888	1,758
Income before income tax expense	580	549	1,146	1,050
Income tax expense	127	124	254	237
NET INCOME	453	425	892	813
Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net interest income	(19)	(9)	(39)	(11)
Noninterest income	4	1	11	8
Noninterest expense	4	4	9	8
Income tax expense	(4)	(4)	(9)	(3)
NET INCOME	$ (15)	$ (8)	$ (28)	$ (8)