BUSINESS OPERATING SEGMENTS - Assets by Segment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Segment Reporting Information [Line Items]
Net interest income	$ 1,410	$ 1,588	$ 2,852	$ 3,231
Noninterest income	553	506	1,070	991
Total revenue	1,963	2,094	3,922	4,222
Noninterest expense	1,301	1,306	2,659	2,602
Profit (loss) before provision (benefit) for credit losses	662	788	1,263	1,620
Provision (benefit) for credit losses	182	176	353	344
Income before income tax expense	480	612	910	1,276
Income tax expense (benefit)	88	134	184	287
NET INCOME	392	478	726	989
Total average assets	219,222	222,373	219,996	222,541
Operating Segments | Consumer Banking
Segment Reporting Information [Line Items]
Net interest income	1,120	1,023	2,213	2,034
Noninterest income	277	268	535	524
Total revenue	1,397	1,291	2,748	2,558
Noninterest expense	915	875	1,818	1,732
Profit (loss) before provision (benefit) for credit losses	482	416	930	826
Provision (benefit) for credit losses	84	68	165	131
Income before income tax expense	398	348	765	695
Income tax expense (benefit)	102	91	197	181
NET INCOME	296	257	568	514
Total average assets	74,295	72,583	74,064	72,230
Operating Segments | Commercial Banking
Segment Reporting Information [Line Items]
Net interest income	494	584	1,008	1,181
Noninterest income	242	207	469	408
Total revenue	736	791	1,477	1,589
Noninterest expense	311	315	628	646
Profit (loss) before provision (benefit) for credit losses	425	476	849	943
Provision (benefit) for credit losses	90	71	171	118
Income before income tax expense	335	405	678	825
Income tax expense (benefit)	76	100	160	201
NET INCOME	259	305	518	624
Total average assets	68,958	77,546	69,529	78,215
Operating Segments | Non-Core
Segment Reporting Information [Line Items]
Net interest income	(31)	(28)	(68)	(43)
Noninterest income	0	0	0	0
Total revenue	(31)	(28)	(68)	(43)
Noninterest expense	26	33	51	65
Profit (loss) before provision (benefit) for credit losses	(57)	(61)	(119)	(108)
Provision (benefit) for credit losses	10	13	29	34
Income before income tax expense	(67)	(74)	(148)	(142)
Income tax expense (benefit)	(17)	(19)	(38)	(37)
NET INCOME	(50)	(55)	(110)	(105)
Total average assets	9,418	14,456	9,986	15,068
Other
Segment Reporting Information [Line Items]
Net interest income	(173)	9	(301)	59
Noninterest income	34	31	66	59
Total revenue	(139)	40	(235)	118
Noninterest expense	49	83	162	159
Profit (loss) before provision (benefit) for credit losses	(188)	(43)	(397)	(41)
Provision (benefit) for credit losses	(2)	24	(12)	61
Income before income tax expense	(186)	(67)	(385)	(102)
Income tax expense (benefit)	(73)	(38)	(135)	(58)
NET INCOME	(113)	(29)	(250)	(44)
Total average assets	$ 66,551	$ 57,788	$ 66,417	$ 57,028