BUSINESS OPERATING SEGMENTS - Schedule of Business Operating Segments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Net interest income	$ 4,614	$ 4,532	$ 4,173
Noninterest income	1,877	1,596	1,534
Total revenue	6,491	6,128	5,707
Noninterest expense	3,847	3,619	3,474
Profit (loss) before provision for credit losses	2,644	2,509	2,233
Provision for credit losses	393	326	321
Income before income tax expense	2,251	2,183	1,912
Income tax expense	460	462	260
NET INCOME	1,791	1,721	1,652
Total average assets	162,176	154,553	149,953
Operating Segments | Consumer Banking
Segment Reporting Information [Line Items]
Net interest income	3,182	3,064	2,651
Noninterest income	1,156	973	905
Total revenue	4,338	4,037	3,556
Noninterest expense	2,851	2,723	2,593
Profit (loss) before provision for credit losses	1,487	1,314	963
Provision for credit losses	325	289	265
Income before income tax expense	1,162	1,025	698
Income tax expense	287	258	246
NET INCOME	875	767	452
Total average assets	66,240	62,444	59,714
Operating Segments | Commercial Banking
Segment Reporting Information [Line Items]
Net interest income	1,466	1,497	1,411
Noninterest income	607	545	538
Total revenue	2,073	2,042	1,949
Noninterest expense	858	813	772
Profit (loss) before provision for credit losses	1,215	1,229	1,177
Provision for credit losses	97	26	19
Income before income tax expense	1,118	1,203	1,158
Income tax expense	248	276	384
NET INCOME	870	927	774
Total average assets	55,947	52,362	49,747
Other
Segment Reporting Information [Line Items]
Net interest income	(34)	(29)	111
Noninterest income	114	78	91
Total revenue	80	49	202
Noninterest expense	138	83	109
Profit (loss) before provision for credit losses	(58)	(34)	93
Provision for credit losses	(29)	11	37
Income before income tax expense	(29)	(45)	56
Income tax expense	(75)	(72)	(370)
NET INCOME	46	27	426
Total average assets	$ 39,989	$ 39,747	$ 40,492