CREDIT QUALITY AND THE ALLOWANCE FOR CREDIT LOSSES - Allowance for Credit Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses, beginning of period	$ 2,098	$ 1,983
Charge-offs	(231)	(171)
Recoveries	50	38
Net charge-offs	(181)	(133)
Provision expense (benefit) for loans and leases	169	167
Allowance for loan and lease losses, end of period	2,086	2,017
Unfunded lending commitments [Roll Forward]
Allowance for unfunded lending commitments, beginning of period	220	257
Provision expense (benefit) for unfunded lending commitments	2	1
Allowance for unfunded lending commitments, end of period	222	258
Total allowance for credit losses, end of period	2,308	2,275
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses, beginning of period	1,250	1,060
Charge-offs	(102)	(59)
Recoveries	17	7
Net charge-offs	(85)	(52)
Provision expense (benefit) for loans and leases	69	103
Allowance for loan and lease losses, end of period	1,234	1,111
Unfunded lending commitments [Roll Forward]
Allowance for unfunded lending commitments, beginning of period	175	207
Provision expense (benefit) for unfunded lending commitments	16	8
Allowance for unfunded lending commitments, end of period	191	215
Total allowance for credit losses, end of period	1,425	1,326
Retail
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses, beginning of period	848	923
Charge-offs	(129)	(112)
Recoveries	33	31
Net charge-offs	(96)	(81)
Provision expense (benefit) for loans and leases	100	64
Allowance for loan and lease losses, end of period	852	906
Unfunded lending commitments [Roll Forward]
Allowance for unfunded lending commitments, beginning of period	45	50
Provision expense (benefit) for unfunded lending commitments	(14)	(7)
Allowance for unfunded lending commitments, end of period	31	43
Total allowance for credit losses, end of period	$ 883	$ 949