CREDIT QUALITY AND THE ALLOWANCE FOR CREDIT LOSSES (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses, beginning of period	$ 2,017	$ 1,720	$ 1,983	$ 1,758
Allowance on PCD loans and leases at acquisition		101		101
Charge-offs	(189)	(91)	(360)	(192)
Recoveries	37	42	75	84
Net charge-offs	(152)	(49)	(285)	(108)
Provision expense (benefit) for loans and leases	179	192	346	213
Allowance for loan and lease losses, end of period	2,044	1,964	2,044	1,964
Unfunded lending commitments [Roll Forward]
Allowance for unfunded lending commitments, beginning of period	258	158	257	176
Provision expense (benefit) for unfunded lending commitments	(3)	24	(2)	6
Allowance on PCD unfunded lending commitments at acquisition		1		1
Allowance for unfunded lending commitments, end of period	255	183	255	183
Total allowance for credit losses, end of period	2,299	2,147	2,299	2,147
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		145		169
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses, beginning of period	1,111	778	1,060	821
Allowance on PCD loans and leases at acquisition		99		99
Charge-offs	(79)	(13)	(138)	(27)
Recoveries	3	3	10	6
Net charge-offs	(76)	(10)	(128)	(21)
Provision expense (benefit) for loans and leases	122	120	225	88
Allowance for loan and lease losses, end of period	1,157	987	1,157	987
Unfunded lending commitments [Roll Forward]
Allowance for unfunded lending commitments, beginning of period	215	147	207	153
Provision expense (benefit) for unfunded lending commitments	(2)	18	6	12
Allowance on PCD unfunded lending commitments at acquisition		1		1
Allowance for unfunded lending commitments, end of period	213	166	213	166
Total allowance for credit losses, end of period	1,370	1,153	1,370	1,153
Commercial | Investors Acquisition
Allowance for Loan and Lease Losses [Roll Forward]
Charge-offs		(33)		(33)
Retail
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan and lease losses, beginning of period	906	942	923	937
Allowance on PCD loans and leases at acquisition		2		2
Charge-offs	(110)	(78)	(222)	(165)
Recoveries	34	39	65	78
Net charge-offs	(76)	(39)	(157)	(87)
Provision expense (benefit) for loans and leases	57	72	121	125
Allowance for loan and lease losses, end of period	887	977	887	977
Unfunded lending commitments [Roll Forward]
Allowance for unfunded lending commitments, beginning of period	43	11	50	23
Provision expense (benefit) for unfunded lending commitments	(1)	6	(8)	(6)
Allowance on PCD unfunded lending commitments at acquisition		0		0
Allowance for unfunded lending commitments, end of period	42	17	42	17
Total allowance for credit losses, end of period	$ 929	$ 994	$ 929	$ 994