BUSINESS OPERATING SEGMENTS - Assets by Segment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Segment Reporting Information [Line Items]
Net interest income	$ 1,147	$ 1,117
Noninterest income	498	542
Total revenue	1,645	1,659
Noninterest expense	1,106	1,018
Profit (loss) before provision (benefit) for credit losses	539	641
Provision (benefit) for credit losses	3	(140)
Income before income tax expense	536	781
Income tax expense (benefit)	116	170
NET INCOME	420	611
Total average assets	188,317	182,569
Operating Segments
Segment Reporting Information [Line Items]
Noninterest income	498	542
Operating Segments | Consumer Banking
Segment Reporting Information [Line Items]
Net interest income	857	863
Noninterest income	257	351
Total revenue	1,114	1,214
Noninterest expense	784	750
Profit (loss) before provision (benefit) for credit losses	330	464
Provision (benefit) for credit losses	49	59
Income before income tax expense	281	405
Income tax expense (benefit)	72	103
NET INCOME	209	302
Total average assets	77,551	75,283
Operating Segments | Commercial Banking
Segment Reporting Information [Line Items]
Net interest income	416	421
Noninterest income	213	170
Total revenue	629	591
Noninterest expense	272	227
Profit (loss) before provision (benefit) for credit losses	357	364
Provision (benefit) for credit losses	12	101
Income before income tax expense	345	263
Income tax expense (benefit)	74	52
NET INCOME	271	211
Total average assets	61,118	57,738
Other
Segment Reporting Information [Line Items]
Net interest income	(126)	(167)
Noninterest income	28	21
Total revenue	(98)	(146)
Noninterest expense	50	41
Profit (loss) before provision (benefit) for credit losses	(148)	(187)
Provision (benefit) for credit losses	(58)	(300)
Income before income tax expense	(90)	113
Income tax expense (benefit)	(30)	15
NET INCOME	(60)	98
Total average assets	$ 49,648	$ 49,548