BUSINESS OPERATING SEGMENTS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Net interest income	$ 4,173	$ 3,758	$ 3,402
Noninterest income	1,534	1,497	1,422
Total revenue	5,707	5,255	4,824
Noninterest expense	3,474	3,352	3,259
Profit (loss) before provision for credit losses	2,233	1,903	1,565
Provision for credit losses	321	369	302
Income before income tax expense	1,912	1,534	1,263
Income tax expense	260	489	423
NET INCOME	1,652	1,045	840
Total average assets	149,953	143,183	135,070
Operating Segments | Consumer Banking
Segment Reporting Information [Line Items]
Net interest income	2,651	2,443	2,198
Noninterest income	905	883	910
Total revenue	3,556	3,326	3,108
Noninterest expense	2,593	2,547	2,456
Profit (loss) before provision for credit losses	963	779	652
Provision for credit losses	265	243	252
Income before income tax expense	698	536	400
Income tax expense	246	191	138
NET INCOME	452	345	262
Total average assets	59,714	56,388	52,848
Operating Segments | Commercial Banking
Segment Reporting Information [Line Items]
Net interest income	1,411	1,288	1,162
Noninterest income	538	466	415
Total revenue	1,949	1,754	1,577
Noninterest expense	772	741	709
Profit (loss) before provision for credit losses	1,177	1,013	868
Provision for credit losses	19	47	(13)
Income before income tax expense	1,158	966	881
Income tax expense	384	335	302
NET INCOME	774	631	579
Total average assets	49,747	47,159	42,800
Other
Segment Reporting Information [Line Items]
Net interest income	111	27	42
Noninterest income	91	148	97
Total revenue	202	175	139
Noninterest expense	109	64	94
Profit (loss) before provision for credit losses	93	111	45
Provision for credit losses	37	79	63
Income before income tax expense	56	32	(18)
Income tax expense	(370)	(37)	(17)
NET INCOME	426	69	(1)
Total average assets	$ 40,492	$ 39,636	$ 39,422