LOANS - Consumer Loans Credit Scores (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	$ 688,922	$ 689,362
Unallocated portfolio layer cumulative basis adjustments	299	93
Consumer loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	389,151	389,197
Unallocated portfolio layer cumulative basis adjustments	670
Consumer loans | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income		3,233
Consumer loans | In North America offices
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	314,375	313,158
Consumer loans | In North America offices | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	2,954	2,897
Consumer loans | In North America offices | 90+ days past due | Banking
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	26,000	29,200
Consumer loans | In offices outside North America
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	74,106	76,039
Consumer loans | In offices outside North America | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	301	336
Consumer loans | In offices outside North America | 90+ days past due | Banking
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	18,200	17,000
Consumer loans | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	312,924	311,671
Consumer loans | Residential mortgages | In North America offices
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	114,126	108,711
Consumer loans | Residential mortgages | In North America offices | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	314	294
Consumer loans | Residential mortgages | In offices outside North America
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	25,702	26,426
Consumer loans | Residential mortgages | In offices outside North America | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	59	69
Consumer loans | Residential mortgages | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	114,126	108,711
Consumer loans | Home equity loans | In North America offices
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	3,242	3,592
Consumer loans | Home equity loans | In North America offices | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	77	85
Consumer loans | Home equity loans | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	3,242	3,592
Consumer loans | Credit cards | In North America offices
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	163,699	164,720
Consumer loans | Credit cards | In North America offices | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	2,510	2,461
Consumer loans | Credit cards | In offices outside North America
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving loans converted to term loans	35	51
Total loans, net of unearned income	12,930	14,233
Consumer loans | Credit cards | In offices outside North America | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	204	227
Consumer loans | Credit cards | Canada
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	623	610
Consumer loans | Credit cards | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	163,076	164,110
Consumer loans | Personal, small business and other
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving loans converted to term loans	25	37
Consumer loans | Personal, small business and other | In North America offices
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	33,308	36,135
Consumer loans | Personal, small business and other | In North America offices | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	53	57
Consumer loans | Personal, small business and other | In offices outside North America
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	35,474	$ 35,380
Consumer loans | Personal, small business and other | In offices outside North America | Internal Investment Grade
Financing Receivable, Credit Quality Indicator [Line Items]
Percentage of loans rated investment grade		92.00%
Consumer loans | Personal, small business and other | In offices outside North America | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	38	$ 40
Consumer loans | Personal, small business and other | Canada
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	828	877
Consumer loans | Personal, small business and other | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	32,480	35,258
Consumer loans | Classifiably Managed and Delinquency Managed | In offices outside North America
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	76,200	77,500
Consumer loans | Less than 660 | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	27,464	26,297
Consumer loans | Less than 660 | Residential mortgages | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	92	163
One year prior to current fiscal year	198	339
Two years prior to current fiscal year	382	270
Three years prior to current fiscal year	323	232
Four years prior to current fiscal year	228	138
Prior	1,602	1,377
Total loans, net of unearned income	2,825	2,519
Consumer loans | Less than 660 | Home equity line of credit (pre-reset) | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	278	300
Consumer loans | Less than 660 | Home equity line of credit (post-reset) | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	61	61
Consumer loans | Less than 660 | Home equity term loans | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
One year prior to current fiscal year	0	0
Two years prior to current fiscal year	0	0
Three years prior to current fiscal year	0	2
Four years prior to current fiscal year	0	0
Prior	49	54
Total loans, net of unearned income	49	56
Consumer loans | Less than 660 | Home equity loans | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	388	417
Consumer loans | Less than 660 | Credit cards | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	22,423	21,899
Consumer loans | Less than 660 | Credit cards | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving loans converted to term loans	1,350	1,011
Total loans, net of unearned income	23,773	22,910
Consumer loans | Less than 660 | Personal, small business and other | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	58	88
One year prior to current fiscal year	136	204
Two years prior to current fiscal year	151	52
Three years prior to current fiscal year	34	6
Four years prior to current fiscal year	3	5
Prior	96	96
Total loans, net of unearned income	478	451
Consumer loans | 660 to 739 | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	78,331	76,958
Consumer loans | 660 to 739 | Residential mortgages | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,729	2,758
One year prior to current fiscal year	2,564	3,423
Two years prior to current fiscal year	3,211	3,107
Three years prior to current fiscal year	2,877	2,143
Four years prior to current fiscal year	2,131	1,382
Prior	4,987	4,122
Total loans, net of unearned income	17,499	16,935
Consumer loans | 660 to 739 | Home equity line of credit (pre-reset) | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	797	905
Consumer loans | 660 to 739 | Home equity line of credit (post-reset) | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	78	76
Consumer loans | 660 to 739 | Home equity term loans | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
One year prior to current fiscal year	0	0
Two years prior to current fiscal year	0	0
Three years prior to current fiscal year	0	1
Four years prior to current fiscal year	1	1
Prior	93	109
Total loans, net of unearned income	94	111
Consumer loans | 660 to 739 | Home equity loans | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	969	1,092
Consumer loans | 660 to 739 | Credit cards | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	58,214	57,479
Consumer loans | 660 to 739 | Credit cards | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving loans converted to term loans	621	490
Total loans, net of unearned income	58,835	57,969
Consumer loans | 660 to 739 | Personal, small business and other | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	279	343
One year prior to current fiscal year	327	351
Two years prior to current fiscal year	216	83
Three years prior to current fiscal year	47	9
Four years prior to current fiscal year	4	7
Prior	155	169
Total loans, net of unearned income	1,028	962
Consumer loans | Greater than or equal to 740 | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	168,654	166,745
Consumer loans | Greater than or equal to 740 | Residential mortgages | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	8,187	14,309
One year prior to current fiscal year	13,613	16,834
Two years prior to current fiscal year	16,299	15,094
Three years prior to current fiscal year	14,699	12,827
Four years prior to current fiscal year	12,356	6,266
Prior	21,098	16,164
Total loans, net of unearned income	86,252	81,494
Consumer loans | Greater than or equal to 740 | Home equity line of credit (pre-reset) | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	1,634	1,873
Consumer loans | Greater than or equal to 740 | Home equity line of credit (post-reset) | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	76	69
Consumer loans | Greater than or equal to 740 | Home equity term loans | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
One year prior to current fiscal year	0	0
Two years prior to current fiscal year	0	1
Three years prior to current fiscal year	1	2
Four years prior to current fiscal year	2	2
Prior	113	131
Total loans, net of unearned income	116	136
Consumer loans | Greater than or equal to 740 | Home equity loans | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	1,826	2,078
Consumer loans | Greater than or equal to 740 | Credit cards | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	78,281	81,168
Consumer loans | Greater than or equal to 740 | Credit cards | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving loans converted to term loans	124	108
Total loans, net of unearned income	78,405	81,276
Consumer loans | Greater than or equal to 740 | Personal, small business and other | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	910	996
One year prior to current fiscal year	700	583
Two years prior to current fiscal year	334	128
Three years prior to current fiscal year	68	14
Four years prior to current fiscal year	6	8
Prior	153	168
Total loans, net of unearned income	2,171	1,897
Consumer loans | Classifiably managed | In offices outside North America
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	18,156	17,007
Consumer loans | Classifiably managed | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	26,022	29,209
Consumer loans | Classifiably managed | Residential mortgages | In offices outside North America
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	0	0
Consumer loans | Classifiably managed | Residential mortgages | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	0	0
Consumer loans | Classifiably managed | Home equity loans | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	0	0
Consumer loans | Classifiably managed | Credit cards | In offices outside North America
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	0	0
Consumer loans | Classifiably managed | Credit cards | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	0	0
Consumer loans | Classifiably managed | Personal, small business and other | In offices outside North America
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	18,156	17,007
Consumer loans | Classifiably managed | Personal, small business and other | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	26,022	29,209
Consumer loans | FICO not available | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	12,453	12,462
Consumer loans | FICO not available | Residential mortgages | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	7,550	7,763
Consumer loans | FICO not available | Home equity loans | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	59	5
Consumer loans | FICO not available | Credit cards | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	2,063	1,955
Consumer loans | FICO not available | Personal, small business and other | U.S. plans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	$ 2,781	$ 2,739