CREDIT QUALITY AND THE ALLOWANCE FOR CREDIT LOSSES - Allowance for Credit Loss (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses, beginning of period	$ 2,125	$ 2,044	$ 2,098	$ 1,983
Charge-offs	(231)	(191)	(685)	(551)
Recoveries	39	38	128	113
Net charge-offs	(192)	(153)	(557)	(438)
Provision expense (benefit) for loans and leases	146	189	538	535
Allowance for loan and lease losses, end of period	2,079	2,080	2,079	2,080
Unfunded lending commitments [Roll Forward]
Allowance for unfunded lending commitments, beginning of period	181	255	220	257
Provision expense (benefit) for unfunded lending commitments	26	(17)	(13)	(19)
Allowance for unfunded lending commitments, end of period	207	238	207	238
Total allowance for credit losses, end of period	2,286	2,318	2,286	2,318
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses, beginning of period	1,282	1,157	1,250	1,060
Charge-offs	(106)	(74)	(308)	(212)
Recoveries	8	4	29	14
Net charge-offs	(98)	(70)	(279)	(198)
Provision expense (benefit) for loans and leases	3	146	216	371
Allowance for loan and lease losses, end of period	1,187	1,233	1,187	1,233
Unfunded lending commitments [Roll Forward]
Allowance for unfunded lending commitments, beginning of period	147	213	175	207
Provision expense (benefit) for unfunded lending commitments	17	(21)	(11)	(15)
Allowance for unfunded lending commitments, end of period	164	192	164	192
Total allowance for credit losses, end of period	1,351	1,425	1,351	1,425
Retail
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses, beginning of period	843	887	848	923
Charge-offs	(125)	(117)	(377)	(339)
Recoveries	31	34	99	99
Net charge-offs	(94)	(83)	(278)	(240)
Provision expense (benefit) for loans and leases	143	43	322	164
Allowance for loan and lease losses, end of period	892	847	892	847
Unfunded lending commitments [Roll Forward]
Allowance for unfunded lending commitments, beginning of period	34	42	45	50
Provision expense (benefit) for unfunded lending commitments	9	4	(2)	(4)
Allowance for unfunded lending commitments, end of period	43	46	43	46
Total allowance for credit losses, end of period	$ 935	$ 893	$ 935	$ 893