LOANS - Performance of Modified Consumer Loans (Details) - Consumer loans - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2024	Dec. 31, 2023
In North America offices
Financing Receivable, Modified [Line Items]
Total modified loans balance	$ 1,413	$ 1,238
Gross credit losses	264	205
In North America offices | Current
Financing Receivable, Modified [Line Items]
Total modified loans balance	1,040	836
In North America offices | 30–89 days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	201	203
In North America offices | 90+ days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	172	199
In offices outside North America
Financing Receivable, Modified [Line Items]
Total modified loans balance	335	404
Gross credit losses	2	5
In offices outside North America | Current
Financing Receivable, Modified [Line Items]
Total modified loans balance	326	392
In offices outside North America | 30–89 days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	8	8
In offices outside North America | 90+ days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	1	4
Residential mortgages | In North America offices
Financing Receivable, Modified [Line Items]
Total modified loans balance	122	164
Gross credit losses	0	0
Residential mortgages | In North America offices | Current
Financing Receivable, Modified [Line Items]
Total modified loans balance	65	70
Residential mortgages | In North America offices | 30–89 days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	24	22
Residential mortgages | In North America offices | 90+ days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	33	72
Residential mortgages | In offices outside North America
Financing Receivable, Modified [Line Items]
Total modified loans balance	297	334
Gross credit losses	1	0
Residential mortgages | In offices outside North America | Current
Financing Receivable, Modified [Line Items]
Total modified loans balance	293	331
Residential mortgages | In offices outside North America | 30–89 days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	3	2
Residential mortgages | In offices outside North America | 90+ days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	1	1
Home equity loans | In North America offices
Financing Receivable, Modified [Line Items]
Total modified loans balance	3	21
Gross credit losses	0	0
Home equity loans | In North America offices | Current
Financing Receivable, Modified [Line Items]
Total modified loans balance	2	14
Home equity loans | In North America offices | 30–89 days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	0	1
Home equity loans | In North America offices | 90+ days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	1	6
Credit cards | In North America offices
Financing Receivable, Modified [Line Items]
Total modified loans balance	1,268	1,039
Gross credit losses	262	204
Credit cards | In North America offices | Current
Financing Receivable, Modified [Line Items]
Total modified loans balance	955	740
Credit cards | In North America offices | 30–89 days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	176	179
Credit cards | In North America offices | 90+ days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	137	120
Credit cards | In offices outside North America
Financing Receivable, Modified [Line Items]
Total modified loans balance	14	43
Gross credit losses	0	4
Credit cards | In offices outside North America | Current
Financing Receivable, Modified [Line Items]
Total modified loans balance	13	37
Credit cards | In offices outside North America | 30–89 days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	1	3
Credit cards | In offices outside North America | 90+ days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	0	3
Personal, small business and other | In North America offices
Financing Receivable, Modified [Line Items]
Total modified loans balance	20	14
Gross credit losses	2	1
Personal, small business and other | In North America offices | Current
Financing Receivable, Modified [Line Items]
Total modified loans balance	18	12
Personal, small business and other | In North America offices | 30–89 days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	1	1
Personal, small business and other | In North America offices | 90+ days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	1	1
Personal, small business and other | In offices outside North America
Financing Receivable, Modified [Line Items]
Total modified loans balance	24	27
Gross credit losses	1	1
Personal, small business and other | In offices outside North America | Current
Financing Receivable, Modified [Line Items]
Total modified loans balance	20	24
Personal, small business and other | In offices outside North America | 30–89 days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	4	3
Personal, small business and other | In offices outside North America | 90+ days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	$ 0	$ 0