LOANS - Types of Consumer Loan Modifications and Their Financial Effect (Details) - Consumer loans - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
In North America offices
Financing Receivable, Impaired [Line Items]
Modifications as % of loans	0.14%	0.11%	0.27%	0.21%
Total modifications balance	$ 444	$ 335	$ 846	$ 624
In North America offices | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	411	276	778	501
In North America offices | Term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	17	16	38	31
In North America offices | Payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	7	30	15	70
In North America offices | Combination: interest rate reduction and term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	9	13	15	22
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	0.03%	0.38%	0.06%	0.43%
Total modifications balance	$ 24	$ 297	$ 47	$ 335
In offices outside North America | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	5	16	11	31
In offices outside North America | Term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	1	2	3	4
In offices outside North America | Payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	11	0	23	0
In offices outside North America | Combination: interest rate reduction and term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	7	4	10	10
In offices outside North America | Combination: term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	275	0	290
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	2	1	$ 2	1
Residential mortgages | In North America offices
Financing Receivable, Impaired [Line Items]
Trial modifications, period			3 months
Trial modifications, amount	11	15	$ 17	26
Loans that had gone through bankruptcy	$ 1	$ 1	$ 3	$ 2
Modifications as % of loans	0.02%	0.05%	0.05%	0.10%
Total modifications balance	$ 26	$ 47	$ 55	$ 100
Weighted-average interest rate reduction %	0.00%	1.00%	0.00%	1.00%
Weighted average term extension	190 months	191 months	187 months	187 months
Weighted average delay in payments	9 months	6 months	9 months	6 months
Residential mortgages | In North America offices | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 0	$ 1	$ 0	$ 1
Residential mortgages | In North America offices | Term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	17	15	38	30
Residential mortgages | In North America offices | Payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	7	29	14	64
Residential mortgages | In North America offices | Combination: interest rate reduction and term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	2	2	3	5
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%	1.03%	0.09%	1.09%
Total modifications balance	$ 12	$ 278	$ 24	$ 296
Weighted-average interest rate reduction %	2.00%	0.00%	2.00%	0.00%
Weighted average term extension	168 months	1 month	183 months	2 months
Weighted average delay in payments	12 months	1 month	12 months	2 months
Residential mortgages | In offices outside North America | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 0	$ 3	$ 0	$ 5
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	11	0	23	0
Residential mortgages | In offices outside North America | Combination: interest rate reduction and term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	1	0	1	1
Residential mortgages | In offices outside North America | Combination: term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	275	0	290
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	0.03%	0.23%	0.03%	0.48%
Total modifications balance	$ 1	$ 9	$ 1	$ 19
Weighted-average interest rate reduction %	1.00%	2.00%	2.00%	2.00%
Weighted average term extension	172 months	119 months	146 months	120 months
Weighted average delay in payments		6 months		6 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	0	6
Home equity loans | In North America offices | Combination: interest rate reduction and term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	1	8	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	$ 28	$ 16	$ 39	$ 26
Credit cards | In North America offices
Financing Receivable, Impaired [Line Items]
Modifications as % of loans	0.25%	0.18%	0.48%	0.33%
Total modifications balance	$ 411	$ 275	$ 777	$ 499
Weighted-average interest rate reduction %	24.00%	22.00%	24.00%	22.00%
Credit cards | In North America offices | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 411	$ 275	$ 777	$ 499
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	0.03%	0.09%	0.06%	0.17%
Total modifications balance	$ 4	$ 12	$ 8	$ 23
Weighted-average interest rate reduction %	24.00%	18.00%	24.00%	18.00%
Credit cards | In offices outside North America | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 4	$ 12	$ 8	$ 23
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	0
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	$ 2	$ 1	$ 2	$ 1
Personal, small business and other | In North America offices
Financing Receivable, Impaired [Line Items]
Modifications as % of loans	0.02%	0.01%	0.04%	0.02%
Total modifications balance	$ 6	$ 4	$ 13	$ 6
Weighted-average interest rate reduction %	8.00%	6.00%	8.00%	6.00%
Weighted average term extension	17 months	13 months	18 months	14 months
Weighted average delay in payments			5 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	1	0	1
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	6	3	11	4
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%	0.04%	0.04%
Total modifications balance	$ 8	$ 7	$ 15	$ 16
Weighted-average interest rate reduction %	6.00%	9.00%	7.00%	8.00%
Weighted average term extension	24 months	20 months	24 months	21 months
Personal, small business and other | In offices outside North America | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 1	$ 1	$ 3	$ 3
Personal, small business and other | In offices outside North America | Term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	1	2	3	4
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	6	4	9	9
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