LOANS - Consumer Loans Credit Scores (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	$ 666,348	$ 657,221
Consumer loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	377,714	368,067
Consumer loans | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	2,792	2,153
Consumer loans | In North America offices
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	302,453	289,014
Consumer loans | In North America offices | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	2,477	1,888
Consumer loans | In North America offices | 90+ days past due | Personal Banking and Wealth Management
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	29,800	31,500
Consumer loans | In offices outside North America
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	75,261	79,053
Consumer loans | In offices outside North America | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	315	265
Consumer loans | In offices outside North America | 90+ days past due | Personal Banking and Wealth Management
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	17,000	17,800
Consumer loans | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	106,369	96,039
Consumer loans | Residential mortgages | In North America offices
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	106,369	96,039
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	294	316
Consumer loans | Residential mortgages | In offices outside North America
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	26,389	28,114
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	72	106
Consumer loans | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	3,796	4,580
Consumer loans | Home equity loans | In North America offices
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	3,796	4,580
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	89	135
Consumer loans | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	155,092	150,098
Consumer loans | Credit cards | In North America offices
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	155,698	150,643
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	2,045	1,415
Consumer loans | Credit cards | In offices outside North America
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving loans converted to term loans	68	75
Total loans, net of unearned income	13,573	12,955
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	202	149
Consumer loans | Credit cards | Canada
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	606	545
Consumer loans | Personal, small business and other
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving loans converted to term loans	42	67
Total loans, net of unearned income	35,691	36,812
Consumer loans | Personal, small business and other | In North America offices
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	36,590	37,752
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	49	22
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	35,299	$ 37,984
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		98.00%
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	41	$ 10
Consumer loans | Personal, small business and other | Canada
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	899	940
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	76,800	80,500
Consumer loans | Less than 680
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	37,121	34,306
Consumer loans | Less than 680 | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	300	691
One year prior to current fiscal year	698	639
Two years prior to current fiscal year	592	431
Three years prior to current fiscal year	412	321
Four years prior to current fiscal year	280	302
Prior	2,073	2,020
Total loans, net of unearned income	4,355	4,404
Consumer loans | Less than 680 | Home equity loans (pre-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	418	552
Consumer loans | Less than 680 | Home equity loans (post-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	74	62
Consumer loans | Less than 680 | Home equity term loans
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	0	1
Four years prior to current fiscal year	1	1
Prior	86	103
Total loans, net of unearned income	87	106
Consumer loans | Less than 680 | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	579	720
Consumer loans | Less than 680 | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	30,570	27,901
Consumer loans | Less than 680 | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving loans converted to term loans	1,013	766
Total loans, net of unearned income	31,583	28,667
Consumer loans | Less than 680 | Personal, small business and other
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	84	247
One year prior to current fiscal year	293	96
Two years prior to current fiscal year	77	15
Three years prior to current fiscal year	9	21
Four years prior to current fiscal year	10	10
Prior	131	126
Total loans, net of unearned income	604	515
Consumer loans | 680 to 760
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	93,182	89,490
Consumer loans | 680 to 760 | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	4,526	7,530
One year prior to current fiscal year	6,331	5,933
Two years prior to current fiscal year	5,574	4,621
Three years prior to current fiscal year	4,235	2,505
Four years prior to current fiscal year	2,367	1,072
Prior	6,980	6,551
Total loans, net of unearned income	30,013	28,212
Consumer loans | 680 to 760 | Home equity loans (pre-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	1,079	1,536
Consumer loans | 680 to 760 | Home equity loans (post-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	76	65
Consumer loans | 680 to 760 | Home equity term loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
One year prior to current fiscal year	0	1
Two years prior to current fiscal year	0	2
Three years prior to current fiscal year	2	2
Four years prior to current fiscal year	1	2
Prior	128	144
Total loans, net of unearned income	131	151
Consumer loans | 680 to 760 | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	1,286	1,752
Consumer loans | 680 to 760 | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	60,462	58,213
Consumer loans | 680 to 760 | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving loans converted to term loans	375	354
Total loans, net of unearned income	60,837	58,567
Consumer loans | 680 to 760 | Personal, small business and other
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	304	546
One year prior to current fiscal year	440	170
Two years prior to current fiscal year	104	20
Three years prior to current fiscal year	11	23
Four years prior to current fiscal year	10	10
Prior	177	190
Total loans, net of unearned income	1,046	959
Consumer loans | Greater than 760
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	128,820	120,733
Consumer loans | Greater than 760 | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	9,067	12,928
One year prior to current fiscal year	13,766	12,672
Two years prior to current fiscal year	12,503	10,936
Three years prior to current fiscal year	10,738	5,445
Four years prior to current fiscal year	5,239	1,899
Prior	13,472	12,649
Total loans, net of unearned income	64,785	56,529
Consumer loans | Greater than 760 | Home equity loans (pre-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	1,745	1,876
Consumer loans | Greater than 760 | Home equity loans (post-reset)
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	51	40
Consumer loans | Greater than 760 | Home equity term loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
One year prior to current fiscal year	0	1
Two years prior to current fiscal year	1	2
Three years prior to current fiscal year	2	2
Four years prior to current fiscal year	1	1
Prior	98	111
Total loans, net of unearned income	102	117
Consumer loans | Greater than 760 | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	1,898	2,033
Consumer loans | Greater than 760 | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	60,592	60,896
Consumer loans | Greater than 760 | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Revolving loans converted to term loans	53	54
Total loans, net of unearned income	60,645	60,950
Consumer loans | Greater than 760 | Personal, small business and other
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	633	800
One year prior to current fiscal year	575	210
Two years prior to current fiscal year	127	30
Three years prior to current fiscal year	16	28
Four years prior to current fiscal year	11	9
Prior	130	144
Total loans, net of unearned income	1,492	1,221
Consumer loans | Classifiably managed
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	29,828	31,478
Consumer loans | Classifiably managed | In offices outside North America
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	16,954	17,762
Consumer loans | Classifiably managed | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	0
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 | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	0
Consumer loans | Classifiably managed | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	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 | Personal, small business and other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	29,828	31,478
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	16,954	17,762
Consumer loans | FICO not available
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	11,997	11,522
Consumer loans | FICO not available | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	7,216	6,894
Consumer loans | FICO not available | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	33	75
Consumer loans | FICO not available | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	2,027	1,914
Consumer loans | FICO not available | Personal, small business and other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	2,721	2,639
Consumer loans | Total loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	$ 300,948	$ 287,529