ALLOWANCE FOR CREDIT LOSSES, NONACCRUAL LOANS AND LEASES, AND CONCENTRATIONS OF CREDIT RISK - Summary of Changes in Allowance for Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses, beginning of period	$ 1,983	$ 1,758
Charge-offs	(171)	(101)
Recoveries	38	42
Net charge-offs	(133)	(59)
Provision expense (benefit) for loans and leases	167	21
Allowance for loan and lease losses, end of period	2,017	1,720
Unfunded lending commitments [Roll Forward]
Allowance for unfunded lending commitments, beginning of period	257	176
Provision expense (benefit) for unfunded lending commitments	1	(18)
Allowance for unfunded lending commitments, end of period	258	158
Total allowance for credit losses, end of period	2,275	1,878
Online Deposit Business And 80 East Coast Branches Of HSBC Bank And Investors
Allowance for Loan and Lease Losses [Roll Forward]
Provision expense (benefit) for loans and leases		24
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses, beginning of period	1,060	821
Charge-offs	(59)	(14)
Recoveries	7	3
Net charge-offs	(52)	(11)
Provision expense (benefit) for loans and leases	103	(32)
Allowance for loan and lease losses, end of period	1,111	778
Unfunded lending commitments [Roll Forward]
Allowance for unfunded lending commitments, beginning of period	207	153
Provision expense (benefit) for unfunded lending commitments	8	(6)
Allowance for unfunded lending commitments, end of period	215	147
Total allowance for credit losses, end of period	1,326	925
Retail
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses, beginning of period	923	937
Charge-offs	(112)	(87)
Recoveries	31	39
Net charge-offs	(81)	(48)
Provision expense (benefit) for loans and leases	64	53
Allowance for loan and lease losses, end of period	906	942
Unfunded lending commitments [Roll Forward]
Allowance for unfunded lending commitments, beginning of period	50	23
Provision expense (benefit) for unfunded lending commitments	(7)	(12)
Allowance for unfunded lending commitments, end of period	43	11
Total allowance for credit losses, end of period	$ 949	$ 953