BUSINESS OPERATING SEGMENTS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net interest income	$ 4,532	$ 4,173	$ 3,758
Noninterest income	1,596	1,534	1,497
Total revenue	6,128	5,707	5,255
Noninterest expense	3,619	3,474	3,352
Profit (loss) before provision for credit losses	2,509	2,233	1,903
Provision for credit losses	326	321	369
Income before income tax expense	2,183	1,912	1,534
Income tax expense	462	260	489
NET INCOME	1,721	1,652	1,045
Total average assets	154,553	149,953	143,183
Operating Segments | Consumer Banking
Segment Reporting Information [Line Items]
Net interest income	3,064	2,651	2,443
Noninterest income	973	905	883
Total revenue	4,037	3,556	3,326
Noninterest expense	2,723	2,593	2,547
Profit (loss) before provision for credit losses	1,314	963	779
Provision for credit losses	289	265	243
Income before income tax expense	1,025	698	536
Income tax expense	258	246	191
NET INCOME	767	452	345
Total average assets	62,444	59,714	56,388
Operating Segments | Commercial Banking
Segment Reporting Information [Line Items]
Net interest income	1,497	1,411	1,288
Noninterest income	545	538	466
Total revenue	2,042	1,949	1,754
Noninterest expense	813	772	741
Profit (loss) before provision for credit losses	1,229	1,177	1,013
Provision for credit losses	26	19	47
Income before income tax expense	1,203	1,158	966
Income tax expense	276	384	335
NET INCOME	927	774	631
Total average assets	52,362	49,747	47,159
Other
Segment Reporting Information [Line Items]
Net interest income	(29)	111	27
Noninterest income	78	91	148
Total revenue	49	202	175
Noninterest expense	83	109	64
Profit (loss) before provision for credit losses	(34)	93	111
Provision for credit losses	11	37	79
Income before income tax expense	(45)	56	32
Income tax expense	(72)	(370)	(37)
NET INCOME	27	426	69
Total average assets	$ 39,747	$ 40,492	$ 39,636