BUSINESS OPERATING SEGMENTS (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Net interest income	$ 1,091	$ 1,005
Noninterest income	371	379
Total revenue	1,462	1,384
Noninterest expense	883	854
Profit before provision for credit losses	579	530
Provision for credit losses	78	96
Income before income tax expense	501	434
Income tax expense	113	114
NET INCOME	388	320
Total average assets	151,523	148,786
Operating Segments | Consumer Banking
Segment Reporting Information [Line Items]
Net interest income	733	638
Noninterest income	222	220
Total revenue	955	858
Noninterest expense	656	647
Profit before provision for credit losses	299	211
Provision for credit losses	72	64
Income before income tax expense	227	147
Income tax expense	57	52
NET INCOME	170	95
Total average assets	61,348	58,660
Operating Segments | Commercial Banking
Segment Reporting Information [Line Items]
Net interest income	357	346
Noninterest income	125	134
Total revenue	482	480
Noninterest expense	208	190
Profit before provision for credit losses	274	290
Provision for credit losses	(4)	19
Income before income tax expense	278	271
Income tax expense	63	91
NET INCOME	215	180
Total average assets	50,393	49,243
Other Non-Segment
Segment Reporting Information [Line Items]
Net interest income	1	21
Noninterest income	24	25
Total revenue	25	46
Noninterest expense	19	17
Profit before provision for credit losses	6	29
Provision for credit losses	10	13
Income before income tax expense	(4)	16
Income tax expense	(7)	(29)
NET INCOME	3	45
Total average assets	$ 39,782	$ 40,883