LOANS - Loan-to-Value Ratios Consumer Loans (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	$ 674,578	$ 689,362
Unallocated portfolio layer cumulative basis adjustments	(113)	93
Consumer loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	381,759	389,197
Unallocated portfolio layer cumulative basis adjustments	(74)
Consumer loans | In offices outside North America
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	75,030	76,039
Consumer loans | Less than or equal to 80% | UNITED STATES
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	101,709	101,290
Consumer loans | Greater than 80% but less than or equal to 100% | UNITED STATES
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	10,276	9,119
Consumer loans | Greater than 100% | UNITED STATES
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	236	207
Consumer loans | LTV not available | UNITED STATES
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	1,810	1,687
Consumer loans | Total | UNITED STATES
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	114,031	112,303
Consumer loans | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	110,592	108,711
Consumer loans | Residential mortgages | UNITED STATES
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	110,592	108,711
Consumer loans | Residential mortgages | In offices outside North America
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	25,926	26,426
Consumer loans | Residential mortgages | Less than or equal to 80% | UNITED STATES
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	2,198	13,907
One year prior to current fiscal year	13,502	17,736
Two years prior to current fiscal year	17,543	18,795
Three years prior to current fiscal year	18,568	16,094
Four years prior to current fiscal year	15,920	8,198
Prior	30,710	23,120
Total loans, net of unearned income	98,441	97,850
Consumer loans | Residential mortgages | Less than or equal to 80% | In offices outside North America
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	672	2,756
One year prior to current fiscal year	2,673	3,229
Two years prior to current fiscal year	3,031	3,257
Three years prior to current fiscal year	2,993	2,286
Four years prior to current fiscal year	2,095	2,525
Prior	9,742	8,000
Total loans, net of unearned income	$ 21,206	$ 22,053
Loan to value ratio	56.00%	55.00%
Consumer loans | Residential mortgages | Greater than 80% but less than or equal to 100% | UNITED STATES
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	$ 733	$ 3,769
One year prior to current fiscal year	4,093	3,900
Two years prior to current fiscal year	3,854	728
Three years prior to current fiscal year	782	306
Four years prior to current fiscal year	343	191
Prior	438	191
Total loans, net of unearned income	10,243	9,085
Consumer loans | Residential mortgages | Greater than 80% but less than or equal to 100% | In offices outside North America
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	120	1,007
One year prior to current fiscal year	865	807
Two years prior to current fiscal year	662	754
Three years prior to current fiscal year	611	454
Four years prior to current fiscal year	387	84
Prior	175	84
Total loans, net of unearned income	2,820	3,190
Consumer loans | Residential mortgages | Greater than 100% | UNITED STATES
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	3
One year prior to current fiscal year	4	52
Two years prior to current fiscal year	84	33
Three years prior to current fiscal year	36	1
Four years prior to current fiscal year	1	26
Prior	49	23
Total loans, net of unearned income	174	138
Consumer loans | Residential mortgages | Greater than 100% | In offices outside North America
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	112
One year prior to current fiscal year	280	439
Two years prior to current fiscal year	560	382
Three years prior to current fiscal year	518	62
Four years prior to current fiscal year	138	2
Prior	8	3
Total loans, net of unearned income	1,504	1,000
Consumer loans | Residential mortgages | LTV not available | UNITED STATES
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	1,734	1,638
Consumer loans | Residential mortgages | LTV not available | In offices outside North America
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	396	183
Consumer loans | Home equity line of credit (pre-reset) | Less than or equal to 80% | UNITED STATES
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	2,799	2,964
Consumer loans | Home equity line of credit (pre-reset) | Greater than 80% but less than or equal to 100% | UNITED STATES
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	29	29
Consumer loans | Home equity line of credit (pre-reset) | Greater than 100% | UNITED STATES
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	51	57
Consumer loans | Home equity line of credit (post-reset) | Less than or equal to 80% | UNITED STATES
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	469	476
Consumer loans | Home equity line of credit (post-reset) | Greater than 80% but less than or equal to 100% | UNITED STATES
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	4	5
Consumer loans | Home equity line of credit (post-reset) | Greater than 100% | UNITED STATES
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	11	12
Consumer loans | Home equity loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	3,439	3,592
Consumer loans | Home equity loans | UNITED STATES
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	3,439	3,592
Consumer loans | Home equity loans | Less than or equal to 80% | UNITED STATES
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	3,268	3,440
Consumer loans | Home equity loans | Greater than 80% but less than or equal to 100% | UNITED STATES
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	33	34
Consumer loans | Home equity loans | Greater than 100% | UNITED STATES
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	62	69
Consumer loans | Home equity loans | LTV not available | UNITED STATES
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	$ 76	$ 49