LOANS - Consumer Loans and Ratios Outside of North America (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 674,578	$ 689,362
Consumer loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	381,759	389,197
Consumer loans | 30–89 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income		3,259
Consumer loans | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income		3,233
Consumer loans | Classifiably managed
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	27,135	29,209
Consumer loans | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	110,592	108,711
Consumer loans | Residential mortgages | Classifiably managed
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	0	0
Consumer loans | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	158,238	164,110
Consumer loans | Credit cards | Classifiably managed
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	0	0
Consumer loans | Personal, small business and other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	33,095	35,258
Consumer loans | Personal, small business and other | Classifiably managed
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	27,135	29,209
In offices outside North America | Consumer loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 75,030	76,039
NCL ratio	1.47%		1.09%
In offices outside North America | Consumer loans | 30–89 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 356	$ 364
Past due ratio	0.61%	0.62%
In offices outside North America | Consumer loans | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 324	$ 336
Past due ratio	0.56%	0.57%
In offices outside North America | Consumer loans | Classifiably managed
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 17,128	$ 17,007
In offices outside North America | Consumer loans | FICO Score, Delinquency Managed Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	57,902	59,032
In offices outside North America | Consumer loans | Classifiably Managed and Delinquency Managed
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	76,500	77,500
In offices outside North America | Consumer loans | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 25,926	26,426
NCL ratio	0.07%		0.11%
In offices outside North America | Consumer loans | Residential mortgages | 30–89 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 52	$ 48
Past due ratio	0.20%	0.18%
In offices outside North America | Consumer loans | Residential mortgages | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 72	$ 69
Past due ratio	0.28%	0.26%
In offices outside North America | Consumer loans | Residential mortgages | Classifiably managed
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 0	$ 0
In offices outside North America | Consumer loans | Residential mortgages | FICO Score, Delinquency Managed Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	25,926	26,426
In offices outside North America | Consumer loans | Residential mortgages | Global Wealth Management Business
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	19,500	19,900
In offices outside North America | Consumer loans | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 13,942	14,233
NCL ratio	5.03%		3.80%
In offices outside North America | Consumer loans | Credit cards | 30–89 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 195	$ 209
Past due ratio	1.40%	1.47%
In offices outside North America | Consumer loans | Credit cards | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 215	$ 227
Past due ratio	1.54%	1.59%
In offices outside North America | Consumer loans | Credit cards | Classifiably managed
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 0	$ 0
In offices outside North America | Consumer loans | Credit cards | FICO Score, Delinquency Managed Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	13,942	14,233
In offices outside North America | Consumer loans | Personal, small business and other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 35,162	35,380
NCL ratio	1.09%		0.87%
In offices outside North America | Consumer loans | Personal, small business and other | 30–89 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 109	$ 107
Past due ratio	0.60%	0.58%
In offices outside North America | Consumer loans | Personal, small business and other | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 37	$ 40
Past due ratio	0.21%	0.22%
In offices outside North America | Consumer loans | Personal, small business and other | Classifiably managed
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 17,128	$ 17,007
In offices outside North America | Consumer loans | Personal, small business and other | FICO Score, Delinquency Managed Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	18,034	18,373
In offices outside North America | Consumer loans | Personal, small business and other | Global Wealth Management Business
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	24,700	24,900
In offices outside North America | Consumer loans | Personal, small business and other | Global Wealth Management Business | Classifiably managed
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income		17,000
In offices outside North America | Consumer loans | Personal, small business and other | Global Wealth Management Business | Classifiably Managed and Delinquency Managed
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 24,700	$ 24,900