LOANS - Types of Consumer Loan Modifications and Their Financial Effect (Details) - Consumer loans - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
In North America offices
Financing Receivable, Impaired [Line Items]
Modifications as % of loans	0.16%	0.13%	0.39%	0.31%
Total modifications balance	$ 507	$ 392	$ 1,219	$ 931
In North America offices | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	472	339	1,124	758
In North America offices | Term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	13	25	47	53
In North America offices | Payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	11	20	24	90
In North America offices | Combination: interest rate reduction and term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	11	8	24	30
In North America offices | Combination: term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	0	0
In North America offices | Combination: interest rate reduction, term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 0	$ 0	$ 0	$ 0
In offices outside North America
Financing Receivable, Impaired [Line Items]
Modifications as % of loans	0.04%	0.37%	0.10%	0.47%
Total modifications balance	$ 27	$ 280	$ 76	$ 356
In offices outside North America | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	8	14	18	35
In offices outside North America | Term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	1	2	4	6
In offices outside North America | Payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	13	7	39	25
In offices outside North America | Combination: interest rate reduction and term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	5	4	15	13
In offices outside North America | Combination: term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	253	0	277
In offices outside North America | Combination: interest rate reduction, term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	0	0
Residential mortgages
Financing Receivable, Impaired [Line Items]
Loans forgiven	1	1	$ 2	1
Residential mortgages | In North America offices
Financing Receivable, Impaired [Line Items]
Trial modifications, period			3 months
Trial modifications, amount	8	12	$ 22	22
Loans that had gone through bankruptcy	$ 2	$ 4	$ 5	$ 6
Modifications as % of loans	0.03%	0.05%	0.07%	0.14%
Total modifications balance	$ 29	$ 48	$ 77	$ 145
Weighted-average interest rate reduction %	1.00%	1.00%	1.00%	1.00%
Weighted average term extension	145 months	220 months	171 months	202 months
Weighted average delay in payments	10 months	6 months	9 months	8 months
Residential mortgages | In North America offices | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 1	$ 0	$ 1	$ 1
Residential mortgages | In North America offices | Term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	13	25	47	53
Residential mortgages | In North America offices | Payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	11	19	22	82
Residential mortgages | In North America offices | Combination: interest rate reduction and term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	4	4	7	9
Residential mortgages | In North America offices | Combination: term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	0	0
Residential mortgages | In North America offices | Combination: interest rate reduction, term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 0	$ 0	$ 0	$ 0
Residential mortgages | In offices outside North America
Financing Receivable, Impaired [Line Items]
Modifications as % of loans	0.05%	0.99%	0.16%	1.15%
Total modifications balance	$ 13	$ 260	$ 41	$ 303
Weighted-average interest rate reduction %	0.00%	0.00%	2.00%	2.00%
Weighted average term extension		1 month	188 months	3 months
Weighted average delay in payments	12 months	1 month	12 months	4 months
Residential mortgages | In offices outside North America | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 0	$ 0	$ 0	$ 0
Residential mortgages | In offices outside North America | Term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	0	0
Residential mortgages | In offices outside North America | Payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	13	7	39	25
Residential mortgages | In offices outside North America | Combination: interest rate reduction and term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	2	1
Residential mortgages | In offices outside North America | Combination: term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	253	0	277
Residential mortgages | In offices outside North America | Combination: interest rate reduction, term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 0	$ 0	$ 0	$ 0
Home equity loans | In North America offices
Financing Receivable, Impaired [Line Items]
Modifications as % of loans	0.00%	0.03%	0.06%	0.55%
Total modifications balance	$ 0	$ 1	$ 2	$ 21
Weighted-average interest rate reduction %	0.00%	2.00%	1.00%	2.00%
Weighted average term extension		146 months	151 months	122 months
Weighted average delay in payments		6 months	9 months	8 months
Home equity loans | In North America offices | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 0	$ 0	$ 0	$ 0
Home equity loans | In North America offices | Term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	0	0
Home equity loans | In North America offices | Payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	1	1	8
Home equity loans | In North America offices | Combination: interest rate reduction and term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	1	13
Home equity loans | In North America offices | Combination: term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	0	0
Home equity loans | In North America offices | Combination: interest rate reduction, term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	0	0
Credit cards
Financing Receivable, Impaired [Line Items]
Loans forgiven	$ 30	$ 17	$ 58	$ 38
Credit cards | In North America offices
Financing Receivable, Impaired [Line Items]
Modifications as % of loans	0.29%	0.22%	0.69%	0.49%
Total modifications balance	$ 471	$ 339	$ 1,122	$ 756
Weighted-average interest rate reduction %	25.00%	22.00%	24.00%	22.00%
Credit cards | In North America offices | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 471	$ 339	$ 1,122	$ 756
Credit cards | In North America offices | Term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	0	0
Credit cards | In North America offices | Payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	0	0
Credit cards | In North America offices | Combination: interest rate reduction and term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	0	0
Credit cards | In North America offices | Combination: term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	0	0
Credit cards | In North America offices | Combination: interest rate reduction, term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 0	$ 0	$ 0	$ 0
Credit cards | In offices outside North America
Financing Receivable, Impaired [Line Items]
Modifications as % of loans	0.05%	0.10%	0.11%	0.24%
Total modifications balance	$ 6	$ 13	$ 14	$ 33
Weighted-average interest rate reduction %	24.00%	18.00%	24.00%	18.00%
Weighted average term extension				28 months
Credit cards | In offices outside North America | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 6	$ 13	$ 14	$ 32
Credit cards | In offices outside North America | Term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	0	0
Credit cards | In offices outside North America | Payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	0	0
Credit cards | In offices outside North America | Combination: interest rate reduction and term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	0	1
Credit cards | In offices outside North America | Combination: term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	0	0
Credit cards | In offices outside North America | Combination: interest rate reduction, term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	0	0
Personal, small business and other
Financing Receivable, Impaired [Line Items]
Loans forgiven	$ 1	$ 1	$ 2	$ 2
Personal, small business and other | In North America offices
Financing Receivable, Impaired [Line Items]
Modifications as % of loans	0.02%	0.01%	0.05%	0.02%
Total modifications balance	$ 7	$ 4	$ 18	$ 9
Weighted-average interest rate reduction %	8.00%	6.00%	8.00%	6.00%
Weighted average term extension	19 months	15 months	18 months	15 months
Weighted average delay in payments			7 months
Personal, small business and other | In North America offices | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 0	$ 0	$ 1	$ 1
Personal, small business and other | In North America offices | Term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	0	0
Personal, small business and other | In North America offices | Payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	1	0
Personal, small business and other | In North America offices | Combination: interest rate reduction and term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	7	4	16	8
Personal, small business and other | In North America offices | Combination: term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	0	0
Personal, small business and other | In North America offices | Combination: interest rate reduction, term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 0	$ 0	$ 0	$ 0
Personal, small business and other | In offices outside North America
Financing Receivable, Impaired [Line Items]
Modifications as % of loans	0.02%	0.02%	0.06%	0.06%
Total modifications balance	$ 8	$ 7	$ 21	$ 20
Weighted-average interest rate reduction %	7.00%	8.00%	7.00%	8.00%
Weighted average term extension	25 months	21 months	24 months	19 months
Personal, small business and other | In offices outside North America | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 2	$ 1	$ 4	$ 3
Personal, small business and other | In offices outside North America | Term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	1	2	4	6
Personal, small business and other | In offices outside North America | Payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	0	0
Personal, small business and other | In offices outside North America | Combination: interest rate reduction and term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	5	4	13	11
Personal, small business and other | In offices outside North America | Combination: term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0	0	0
Personal, small business and other | In offices outside North America | Combination: interest rate reduction, term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 0	$ 0	$ 0	$ 0