BUSINESS OPERATING SEGMENTS - Assets by Segment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Segment Reporting Information [Line Items]
Net interest income	$ 1,643	$ 1,147
Noninterest income	485	498
Total revenue	2,128	1,645
Noninterest expense	1,296	1,106
Profit (loss) before provision (benefit) for credit losses	832	539
Provision (benefit) for credit losses	168	3
Income before income tax expense	664	536
Income tax expense (benefit)	153	116
NET INCOME	511	420
Total average assets	222,711	188,317
Operating Segments
Segment Reporting Information [Line Items]
Noninterest income	485	498
Operating Segments | Consumer Banking
Segment Reporting Information [Line Items]
Net interest income	1,096	857
Noninterest income	256	257
Total revenue	1,352	1,114
Noninterest expense	889	784
Profit (loss) before provision (benefit) for credit losses	463	330
Provision (benefit) for credit losses	83	49
Income before income tax expense	380	281
Income tax expense (benefit)	99	72
NET INCOME	281	209
Total average assets	87,558	77,551
Operating Segments | Commercial Banking
Segment Reporting Information [Line Items]
Net interest income	597	416
Noninterest income	201	213
Total revenue	798	629
Noninterest expense	331	272
Profit (loss) before provision (benefit) for credit losses	467	357
Provision (benefit) for credit losses	47	12
Income before income tax expense	420	345
Income tax expense (benefit)	101	74
NET INCOME	319	271
Total average assets	78,891	61,118
Other
Segment Reporting Information [Line Items]
Net interest income	(50)	(126)
Noninterest income	28	28
Total revenue	(22)	(98)
Noninterest expense	76	50
Profit (loss) before provision (benefit) for credit losses	(98)	(148)
Provision (benefit) for credit losses	38	(58)
Income before income tax expense	(136)	(90)
Income tax expense (benefit)	(47)	(30)
NET INCOME	(89)	(60)
Total average assets	$ 56,262	$ 49,648