LOANS - Performance of Modified Consumer Loans (Details) - Consumer loans - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2024	Dec. 31, 2023
In North America offices
Financing Receivable, Modified [Line Items]
Total modified loans balance	$ 1,495	$ 1,238
Gross credit losses	282	205
In North America offices | Current
Financing Receivable, Modified [Line Items]
Total modified loans balance	1,102	836
In North America offices | 30–89 days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	224	203
In North America offices | 90+ days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	169	199
In offices outside North America
Financing Receivable, Modified [Line Items]
Total modified loans balance	132	404
Gross credit losses	2	5
In offices outside North America | Current
Financing Receivable, Modified [Line Items]
Total modified loans balance	122	392
In offices outside North America | 30–89 days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	7	8
In offices outside North America | 90+ days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	3	4
Residential mortgages | In North America offices
Financing Receivable, Modified [Line Items]
Total modified loans balance	99	164
Gross credit losses	0	0
Residential mortgages | In North America offices | Current
Financing Receivable, Modified [Line Items]
Total modified loans balance	49	70
Residential mortgages | In North America offices | 30–89 days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	18	22
Residential mortgages | In North America offices | 90+ days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	32	72
Residential mortgages | In offices outside North America
Financing Receivable, Modified [Line Items]
Total modified loans balance	90	334
Gross credit losses	1	0
Residential mortgages | In offices outside North America | Current
Financing Receivable, Modified [Line Items]
Total modified loans balance	87	331
Residential mortgages | In offices outside North America | 30–89 days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	2	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	2	21
Gross credit losses	0	0
Home equity loans | In North America offices | Current
Financing Receivable, Modified [Line Items]
Total modified loans balance	1	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	1,371	1,039
Gross credit losses	280	204
Credit cards | In North America offices | Current
Financing Receivable, Modified [Line Items]
Total modified loans balance	1,032	740
Credit cards | In North America offices | 30–89 days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	204	179
Credit cards | In North America offices | 90+ days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	135	120
Credit cards | In offices outside North America
Financing Receivable, Modified [Line Items]
Total modified loans balance	17	43
Gross credit losses	0	4
Credit cards | In offices outside North America | Current
Financing Receivable, Modified [Line Items]
Total modified loans balance	15	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	1	3
Personal, small business and other | In North America offices
Financing Receivable, Modified [Line Items]
Total modified loans balance	23	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	20	12
Personal, small business and other | In North America offices | 30–89 days past due
Financing Receivable, Modified [Line Items]
Total modified loans balance	2	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	25	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	$ 1	$ 0