Allowance for Credit Losses - Summary (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Allowance for loan losses
Beginning balance	$ 22,420	$ 19,726	$ 19,726
Gross charge-offs	2,381	1,451
Gross recoveries collected	(425)	(314)
Net charge-offs/(recoveries)	1,956	1,137
Provision for loan losses	1,887	2,047
Other	0	4
Ending balance	22,351	20,053	22,420
Allowance for lending-related commitments
Beginning balance	1,974	2,382	2,382
Provision for lending-related commitments	(60)	(13)
Other	2	1
Ending balance	1,916	2,370	1,974
Total allowance for investment securities	154	90	128
Total allowance for credit losses	24,421	22,513
Allowance for loan losses by impairment methodology
Asset-specific	(359)	(593)
Portfolio-based	22,710	20,646
Total allowance for loan losses	22,351	20,053	22,420
Loans by impairment methodology
Asset-specific	6,143	5,749
Portfolio-based	1,257,950	1,079,101
Total retained loans	1,264,093	1,084,850	1,280,870
Allowance for lending-related commitments by impairment methodology
Asset-specific	85	45
Portfolio-based	1,831	2,325
Total allowance for lending-related commitments	1,916	2,370	1,974
Off-Balance Sheet Lending-Related Financial Instruments, Guarantees and Other Commitments [Abstract]
Asset-specific	390	401
Portfolio-based	540,257	488,169
Total lending-related commitments	540,647	488,570
Corporate
Off-Balance Sheet Lending-Related Financial Instruments, Guarantees and Other Commitments [Abstract]
Allowance for Credit Loss, Receivable, Other		241
CIB
Off-Balance Sheet Lending-Related Financial Instruments, Guarantees and Other Commitments [Abstract]
Allowance for credit losses associated with accounts receivable	274	20
Cumulative effect of change in accounting principles | Accounting Standards Update 2022-02
Allowance for loan losses
Beginning balance		(587)	(587)
Allowance for loan losses by impairment methodology
Total allowance for loan losses
Collateral-dependent loans
Allowance for loan losses
Net charge-offs/(recoveries)	50	22
Collateral-dependent loans
Loans measured at fair value of collateral less cost to sell	4,391	4,125
Consumer, excluding credit card
Allowance for loan losses
Beginning balance	1,856	2,040	2,040
Gross charge-offs	331	235
Gross recoveries collected	(148)	(103)
Net charge-offs/(recoveries)	183	132
Provision for loan losses	56	247
Other	1	0
Ending balance	1,730	1,666	1,856
Allowance for lending-related commitments
Beginning balance	75	76	76
Provision for lending-related commitments	21	1
Other	0	0
Ending balance	96	77	75
Total allowance for credit losses	1,826	1,743
Allowance for loan losses by impairment methodology
Asset-specific	(873)	(1,030)
Portfolio-based	2,603	2,696
Total allowance for loan losses	1,730	1,666	1,856
Loans by impairment methodology
Asset-specific	3,216	3,560
Portfolio-based	386,376	296,887
Total retained loans	389,592	300,447	397,275
Allowance for lending-related commitments by impairment methodology
Asset-specific	0	0
Portfolio-based	96	77
Total allowance for lending-related commitments	96	77	75
Off-Balance Sheet Lending-Related Financial Instruments, Guarantees and Other Commitments [Abstract]
Asset-specific	0	0
Portfolio-based	28,994	21,569
Total lending-related commitments	28,994	21,569
Credit card lending-related commitments not permitted to have an allowance for credit losses	17,700	16,000
Consumer, excluding credit card | Cumulative effect of change in accounting principles | Accounting Standards Update 2022-02
Allowance for loan losses
Beginning balance		(489)	(489)
Allowance for loan losses by impairment methodology
Total allowance for loan losses
Consumer, excluding credit card | Collateral-dependent loans
Allowance for loan losses
Net charge-offs/(recoveries)	3	4
Collateral-dependent loans
Loans measured at fair value of collateral less cost to sell	3,260	3,539
Credit card
Allowance for loan losses
Beginning balance	12,450	11,200	11,200
Gross charge-offs	1,914	1,111
Gross recoveries collected	(227)	(189)
Net charge-offs/(recoveries)	1,687	922
Provision for loan losses	1,837	1,222
Other	0	0
Ending balance	12,600	11,400	12,450
Allowance for lending-related commitments
Beginning balance	0	0	0
Provision for lending-related commitments	0	0
Other	0	0
Ending balance	0	0	0
Total allowance for credit losses	12,600	11,400
Allowance for loan losses by impairment methodology
Asset-specific	0	0
Portfolio-based	12,600	11,400
Total allowance for loan losses	12,600	11,400	12,450
Loans by impairment methodology
Asset-specific	0	0
Portfolio-based	206,740	180,079
Total retained loans	206,740	180,079
Allowance for lending-related commitments by impairment methodology
Asset-specific	0	0
Portfolio-based	0	0
Total allowance for lending-related commitments	0	0	0
Off-Balance Sheet Lending-Related Financial Instruments, Guarantees and Other Commitments [Abstract]
Asset-specific	0	0
Portfolio-based	0	0
Total lending-related commitments	0	0
Credit card lending-related commitments not permitted to have an allowance for credit losses	943,900	861,200
Credit card | Cumulative effect of change in accounting principles | Accounting Standards Update 2022-02
Allowance for loan losses
Beginning balance		(100)	(100)
Allowance for loan losses by impairment methodology
Total allowance for loan losses
Credit card | Collateral-dependent loans
Allowance for loan losses
Net charge-offs/(recoveries)	0	0
Collateral-dependent loans
Loans measured at fair value of collateral less cost to sell	0	0
Wholesale
Allowance for loan losses
Beginning balance	8,114	6,486	6,486
Gross charge-offs	136	105
Gross recoveries collected	(50)	(22)
Net charge-offs/(recoveries)	86	83
Provision for loan losses	(6)	578
Other	(1)	4
Ending balance	8,021	6,987	8,114
Allowance for lending-related commitments
Beginning balance	1,899	2,306	2,306
Provision for lending-related commitments	(81)	(14)
Other	2	1
Ending balance	1,820	2,293	1,899
Total allowance for credit losses	9,841	9,280
Allowance for loan losses by impairment methodology
Asset-specific	514	437
Portfolio-based	7,507	6,550
Total allowance for loan losses	8,021	6,987	8,114
Loans by impairment methodology
Asset-specific	2,927	2,189
Portfolio-based	664,834	602,135
Total retained loans	667,761	604,324	672,472
Allowance for lending-related commitments by impairment methodology
Asset-specific	85	45
Portfolio-based	1,735	2,248
Total allowance for lending-related commitments	1,820	2,293	1,899
Off-Balance Sheet Lending-Related Financial Instruments, Guarantees and Other Commitments [Abstract]
Asset-specific	390	401
Portfolio-based	511,263	466,600
Total lending-related commitments	511,653	467,001
Credit card lending-related commitments not permitted to have an allowance for credit losses	20,900	17,500
Wholesale | Cumulative effect of change in accounting principles | Accounting Standards Update 2022-02
Allowance for loan losses
Beginning balance		2	$ 2
Allowance for loan losses by impairment methodology
Total allowance for loan losses
Wholesale | Collateral-dependent loans
Allowance for loan losses
Net charge-offs/(recoveries)	47	18
Collateral-dependent loans
Loans measured at fair value of collateral less cost to sell	$ 1,131	$ 586