BUSINESS OPERATING SEGMENTS - Assets by Segment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Segment Reporting Information [Line Items]
Net interest income	$ 1,588	$ 1,505	$ 3,231	$ 2,652
Noninterest income	506	494	991	992
Total revenue	2,094	1,999	4,222	3,644
Noninterest expense	1,306	1,305	2,602	2,411
Profit (loss) before provision (benefit) for credit losses	788	694	1,620	1,233
Provision (benefit) for credit losses	176	216	344	219
Income before income tax expense	612	478	1,276	1,014
Income tax expense (benefit)	134	114	287	230
NET INCOME	478	364	989	784
Total average assets	222,373	220,967	222,541	204,732
Operating Segments | Consumer Banking
Segment Reporting Information [Line Items]
Net interest income	1,104	995	2,200	1,852
Noninterest income	268	280	524	537
Total revenue	1,372	1,275	2,724	2,389
Noninterest expense	908	881	1,797	1,665
Profit (loss) before provision (benefit) for credit losses	464	394	927	724
Provision (benefit) for credit losses	82	39	165	88
Income before income tax expense	382	355	762	636
Income tax expense (benefit)	100	90	199	162
NET INCOME	282	265	563	474
Total average assets	87,040	88,881	87,298	83,247
Operating Segments | Commercial Banking
Segment Reporting Information [Line Items]
Net interest income	584	534	1,181	950
Noninterest income	207	221	408	434
Total revenue	791	755	1,589	1,384
Noninterest expense	315	308	646	580
Profit (loss) before provision (benefit) for credit losses	476	447	943	804
Provision (benefit) for credit losses	71	10	118	22
Income before income tax expense	405	437	825	782
Income tax expense (benefit)	100	96	201	170
NET INCOME	305	341	624	612
Total average assets	77,546	78,638	78,215	69,927
Other
Segment Reporting Information [Line Items]
Net interest income	(100)	(24)	(150)	(150)
Noninterest income	31	(7)	59	21
Total revenue	(69)	(31)	(91)	(129)
Noninterest expense	83	116	159	166
Profit (loss) before provision (benefit) for credit losses	(152)	(147)	(250)	(295)
Provision (benefit) for credit losses	23	167	61	109
Income before income tax expense	(175)	(314)	(311)	(404)
Income tax expense (benefit)	(66)	(72)	(113)	(102)
NET INCOME	(109)	(242)	(198)	(302)
Total average assets	$ 57,787	$ 53,448	$ 57,028	$ 51,558