BUSINESS OPERATING SEGMENTS - Assets by Segment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information [Line Items]
Net interest income	$ 1,442	$ 1,643
Noninterest income	517	485
Total revenue	1,959	2,128
Noninterest expense	1,358	1,296
Profit (loss) before provision (benefit) for credit losses	601	832
Provision (benefit) for credit losses	171	168
Income before income tax expense	430	664
Income tax expense (benefit)	96	153
NET INCOME	334	511
Total average assets	220,770	222,711
Operating Segments | Consumer Banking
Segment Reporting Information [Line Items]
Net interest income	1,093	1,011
Noninterest income	258	256
Total revenue	1,351	1,267
Noninterest expense	903	857
Profit (loss) before provision (benefit) for credit losses	448	410
Provision (benefit) for credit losses	81	63
Income before income tax expense	367	347
Income tax expense (benefit)	95	90
NET INCOME	272	257
Total average assets	73,833	71,872
Operating Segments | Commercial Banking
Segment Reporting Information [Line Items]
Net interest income	514	597
Noninterest income	227	201
Total revenue	741	798
Noninterest expense	317	331
Profit (loss) before provision (benefit) for credit losses	424	467
Provision (benefit) for credit losses	81	47
Income before income tax expense	343	420
Income tax expense (benefit)	84	101
NET INCOME	259	319
Total average assets	70,100	78,891
Operating Segments | Non-Core
Segment Reporting Information [Line Items]
Net interest income	(37)	(15)
Noninterest income	0	0
Total revenue	(37)	(15)
Noninterest expense	25	32
Profit (loss) before provision (benefit) for credit losses	(62)	(47)
Provision (benefit) for credit losses	19	21
Income before income tax expense	(81)	(68)
Income tax expense (benefit)	(21)	(18)
NET INCOME	(60)	(50)
Total average assets	10,554	15,686
Other
Segment Reporting Information [Line Items]
Net interest income	(128)	50
Noninterest income	32	28
Total revenue	(96)	78
Noninterest expense	113	76
Profit (loss) before provision (benefit) for credit losses	(209)	2
Provision (benefit) for credit losses	(10)	37
Income before income tax expense	(199)	(35)
Income tax expense (benefit)	(62)	(20)
NET INCOME	(137)	(15)
Total average assets	$ 66,283	$ 56,262