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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net interest income	$ 1,121	$ 1,026	$ 2,212	$ 2,031
Provision for credit losses	85	70	163	166
Noninterest income	388	370	759	749
Noninterest expense	875	864	1,758	1,718
Income before income tax expense	549	462	1,050	896
Income tax expense	124	144	237	258
NET INCOME	425	318	813	638
Amount Reclassified from AOCI
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net interest income	(9)	7	(11)	17
Noninterest income	1	(1)	8	2
Noninterest expense	4	4	8	9
Income tax expense	(4)	0	(3)	3
NET INCOME	$ (8)	$ 2	$ (8)	$ 7