LOANS - Consumer Loans and Ratios Outside of North America (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 666,348	$ 657,221
Consumer loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	377,714	368,067
Consumer loans | 30–89 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	2,951	2,372
Consumer loans | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	2,792	2,153
Consumer loans | Classifiably managed
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	29,828	31,478
Consumer loans | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	106,369	96,039
Consumer loans | Residential mortgages | Classifiably managed
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	0
Consumer loans | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	155,092	150,098
Consumer loans | Credit cards | Classifiably managed
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	0
Consumer loans | Personal, small business and other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	35,691	36,812
Consumer loans | Personal, small business and other | Classifiably managed
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	29,828	31,478
In offices outside North America | Consumer loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 75,261	79,053
NCL ratio	1.24%		0.91%
In offices outside North America | Consumer loans | 30–89 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 345	$ 314
Past due ratio	0.59%	0.51%
In offices outside North America | Consumer loans | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 315	$ 265
Past due ratio	0.54%	0.43%
In offices outside North America | Consumer loans | Classifiably managed
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 16,954	$ 17,762
In offices outside North America | Consumer loans | FICO Score, Delinquency Managed Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	58,307	61,291
In offices outside North America | Consumer loans | Classifiably Managed and Delinquency Managed
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	76,800	80,500
In offices outside North America | Consumer loans | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 26,389	28,114
NCL ratio	(0.01%)		0.18%
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	$ 49	$ 62
Past due ratio	0.19%	0.22%
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	$ 106
Past due ratio	0.27%	0.38%
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	26,389	28,114
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	20,000	19,800
In offices outside North America | Consumer loans | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 13,573	12,955
NCL ratio	4.35%		3.22%
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	$ 192	$ 147
Past due ratio	1.41%	1.13%
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	$ 202	$ 149
Past due ratio	1.49%	1.15%
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	13,573	12,955
In offices outside North America | Consumer loans | Personal, small business and other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 35,299	37,984
NCL ratio	0.99%		0.74%
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	$ 104	$ 105
Past due ratio	0.57%	0.52%
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	$ 41	$ 10
Past due ratio	0.22%	0.05%
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	$ 16,954	$ 17,762
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	18,345	20,222
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	24,900	26,600
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		17,800
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	$ 24,900	$ 26,600