LOANS - Types of Consumer Loan Modifications and Their Financial Effect (Details) - Consumer loans - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
In North America offices
Financing Receivable, Impaired [Line Items]
Modifications as % of loans	0.19%	0.16%
Total modifications balance	$ 590	$ 487
In North America offices | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	505	449
In North America offices | Term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	11	24
In North America offices | Payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	57	7
In North America offices | Combination: interest rate reduction and term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	17	7
In North America offices | Combination: term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	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
In offices outside North America
Financing Receivable, Impaired [Line Items]
Modifications as % of loans	0.03%	0.04%
Total modifications balance	$ 24	$ 30
In offices outside North America | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	6	11
In offices outside North America | Term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	1	1
In offices outside North America | Payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	11	14
In offices outside North America | Combination: interest rate reduction and term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	6	4
In offices outside North America | Combination: term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0
In offices outside North America | Combination: interest rate reduction, term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0
Residential mortgages
Financing Receivable, Impaired [Line Items]
Loans forgiven	$ 1	1
Residential mortgages | In North America offices
Financing Receivable, Impaired [Line Items]
Trial modifications, period	3 months
Trial modifications, amount	$ 14	11
Loans that had gone through bankruptcy	$ 3	$ 2
Modifications as % of loans	0.06%	0.03%
Total modifications balance	$ 74	$ 31
Weighted-average interest rate reduction %	1.00%	1.00%
Weighted average term extension	129 months	189 months
Weighted average delay in payments	7 months	10 months
Residential mortgages | In North America offices | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 1	$ 0
Residential mortgages | In North America offices | Term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	11	24
Residential mortgages | In North America offices | Payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	55	6
Residential mortgages | In North America offices | Combination: interest rate reduction and term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	7	1
Residential mortgages | In North America offices | Combination: term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	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
Residential mortgages | In offices outside North America
Financing Receivable, Impaired [Line Items]
Modifications as % of loans	0.05%	0.06%
Total modifications balance	$ 13	$ 15
Weighted-average interest rate reduction %	2.00%	2.00%
Weighted average term extension	192 months	183 months
Weighted average delay in payments	12 months	12 months
Residential mortgages | In offices outside North America | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 0	$ 0
Residential mortgages | In offices outside North America | Term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0
Residential mortgages | In offices outside North America | Payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	11	14
Residential mortgages | In offices outside North America | Combination: interest rate reduction and term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	2	1
Residential mortgages | In offices outside North America | Combination: term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0
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
Home equity loans | In North America offices
Financing Receivable, Impaired [Line Items]
Modifications as % of loans	0.03%	0.00%
Total modifications balance	$ 1	$ 0
Weighted-average interest rate reduction %	0.00%	0.00%
Weighted average delay in payments	8 months
Home equity loans | In North America offices | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 0	$ 0
Home equity loans | In North America offices | Term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0
Home equity loans | In North America offices | Payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	1	0
Home equity loans | In North America offices | Combination: interest rate reduction and term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0
Home equity loans | In North America offices | Combination: term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	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
Credit cards
Financing Receivable, Impaired [Line Items]
Loans forgiven	$ 32	$ 25
Credit cards | In North America offices
Financing Receivable, Impaired [Line Items]
Modifications as % of loans	0.31%	0.28%
Total modifications balance	$ 505	$ 448
Weighted-average interest rate reduction %	25.00%	24.00%
Weighted average delay in payments	4 months
Credit cards | In North America offices | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 504	$ 448
Credit cards | In North America offices | Term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0
Credit cards | In North America offices | Payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	1	0
Credit cards | In North America offices | Combination: interest rate reduction and term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0
Credit cards | In North America offices | Combination: term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	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
Credit cards | In offices outside North America
Financing Receivable, Impaired [Line Items]
Modifications as % of loans	0.04%	0.06%
Total modifications balance	$ 5	$ 9
Weighted-average interest rate reduction %	24.00%	20.00%
Credit cards | In offices outside North America | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 5	$ 9
Credit cards | In offices outside North America | Term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0
Credit cards | In offices outside North America | Payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	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
Credit cards | In offices outside North America | Combination: term extension and payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	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
Personal, small business and other
Financing Receivable, Impaired [Line Items]
Loans forgiven	$ 2	$ 3
Personal, small business and other | In North America offices
Financing Receivable, Impaired [Line Items]
Modifications as % of loans	0.03%	0.02%
Total modifications balance	$ 10	$ 8
Weighted-average interest rate reduction %	8.00%	7.00%
Weighted average term extension	19 months	18 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	$ 1
Personal, small business and other | In North America offices | Term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	0
Personal, small business and other | In North America offices | Payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	0	1
Personal, small business and other | In North America offices | Combination: interest rate reduction and term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	10	6
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
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
Personal, small business and other | In offices outside North America
Financing Receivable, Impaired [Line Items]
Modifications as % of loans	0.02%	0.02%
Total modifications balance	$ 6	$ 6
Weighted-average interest rate reduction %	8.00%	8.00%
Weighted average term extension	23 months	20 months
Personal, small business and other | In offices outside North America | Interest rate reduction
Financing Receivable, Impaired [Line Items]
Total modifications balance	$ 1	$ 2
Personal, small business and other | In offices outside North America | Term extension
Financing Receivable, Impaired [Line Items]
Total modifications balance	1	1
Personal, small business and other | In offices outside North America | Payment delay
Financing Receivable, Impaired [Line Items]
Total modifications balance	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	4	3
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
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