BUSINESS OPERATING SEGMENTS (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Net interest income	$ 1,160	$ 1,091
Noninterest income	428	371
Total revenue	1,588	1,462
Noninterest expense	937	883
Profit before provision for credit losses	651	579
Provision for credit losses	85	78
Income before income tax expense	566	501
Income tax expense (benefit)	127	113
NET INCOME	439	388
Total average assets	160,415	151,523
Operating Segments | Consumer Banking
Segment Reporting Information [Line Items]
Net interest income	788	733
Noninterest income	247	222
Total revenue	1,035	955
Noninterest expense	700	656
Profit before provision for credit losses	335	299
Provision for credit losses	67	72
Income before income tax expense	268	227
Income tax expense (benefit)	66	57
NET INCOME	202	170
Total average assets	65,007	61,348
Operating Segments | Commercial Banking
Segment Reporting Information [Line Items]
Net interest income	372	357
Noninterest income	150	125
Total revenue	522	482
Noninterest expense	209	208
Profit before provision for credit losses	313	274
Provision for credit losses	21	(4)
Income before income tax expense	292	278
Income tax expense (benefit)	65	63
NET INCOME	227	215
Total average assets	55,630	50,393
Other
Segment Reporting Information [Line Items]
Net interest income	0	1
Noninterest income	31	24
Total revenue	31	25
Noninterest expense	28	19
Profit before provision for credit losses	3	6
Provision for credit losses	(3)	10
Income before income tax expense	6	(4)
Income tax expense (benefit)	(4)	(7)
NET INCOME	10	3
Total average assets	$ 39,778	$ 39,782