BUSINESS OPERATING SEGMENTS - Assets by Segment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Segment Reporting Information [Line Items]
Net interest income	$ 1,522	$ 1,665	$ 4,753	$ 4,317
Noninterest income	492	512	1,483	1,504
Total revenue	2,014	2,177	6,236	5,821
Noninterest expense	1,293	1,241	3,895	3,652
Profit (loss) before provision (benefit) for credit losses	721	936	2,341	2,169
Provision (benefit) for credit losses	172	123	516	342
Income before income tax expense	549	813	1,825	1,827
Income tax expense (benefit)	119	177	406	407
NET INCOME	430	636	1,419	1,420
Total average assets	220,162	225,473	221,739	211,722
Operating Segments | Consumer Banking
Segment Reporting Information [Line Items]
Net interest income	1,067	989	3,101	2,635
Noninterest income	278	270	802	807
Total revenue	1,345	1,259	3,903	3,442
Noninterest expense	905	828	2,637	2,424
Profit (loss) before provision (benefit) for credit losses	440	431	1,266	1,018
Provision (benefit) for credit losses	67	47	198	117
Income before income tax expense	373	384	1,068	901
Income tax expense (benefit)	97	98	278	230
NET INCOME	276	286	790	671
Total average assets	72,964	71,631	72,477	66,793
Operating Segments | Commercial Banking
Segment Reporting Information [Line Items]
Net interest income	560	558	1,741	1,508
Noninterest income	180	213	588	647
Total revenue	740	771	2,329	2,155
Noninterest expense	325	325	971	905
Profit (loss) before provision (benefit) for credit losses	415	446	1,358	1,250
Provision (benefit) for credit losses	67	12	185	34
Income before income tax expense	348	434	1,173	1,216
Income tax expense (benefit)	88	100	289	270
NET INCOME	260	334	884	946
Total average assets	74,997	80,067	77,130	73,344
Operating Segments | Non-Core
Segment Reporting Information [Line Items]
Net interest income	(41)	70	(84)	359
Noninterest income	0	0	0	0
Total revenue	(41)	70	(84)	359
Noninterest expense	30	36	95	105
Profit (loss) before provision (benefit) for credit losses	(71)	34	(179)	254
Provision (benefit) for credit losses	20	14	54	33
Income before income tax expense	(91)	20	(233)	221
Income tax expense (benefit)	(24)	4	(61)	56
NET INCOME	(67)	16	(172)	165
Total average assets	13,113	17,929	14,409	18,582
Other
Segment Reporting Information [Line Items]
Net interest income	(64)	48	(5)	(185)
Noninterest income	34	29	93	50
Total revenue	(30)	77	88	(135)
Noninterest expense	33	52	192	218
Profit (loss) before provision (benefit) for credit losses	(63)	25	(104)	(353)
Provision (benefit) for credit losses	18	50	79	158
Income before income tax expense	(81)	(25)	(183)	(511)
Income tax expense (benefit)	(42)	(25)	(100)	(149)
NET INCOME	(39)	0	(83)	(362)
Total average assets	$ 59,088	$ 55,846	$ 57,723	$ 53,003