Loans - Wholesale Loan Portfolio, Internal Risk Ratings (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 960,506	$ 945,601	$ 969,415
Wholesale
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 514,947	$ 481,678	$ 477,023
% of investment-grade to total retained loans	73.65%	75.45%
% of total criticized to total retained loans	3.62%	1.60%
% of criticized nonaccrual to total retained loans	0.64%	0.22%
Net charge-offs/(recoveries)	$ 799	$ 415
% of net charge-offs/(recoveries) to end-of-period retained loans	0.16%	0.09%
Wholesale | Current and less than 30 days past due and still accruing
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 508,707	$ 479,599
Wholesale | 30–89 days past due and still accruing
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	2,865	979
Wholesale | 90 or more days past due and still accruing
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	57	43
Wholesale | Investment-grade
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	379,273	363,444
Wholesale | Investment-grade | Paycheck Protection Program (PPP)
Loans and Leases Receivable Disclosure [Line Items]
Term loans originated in 2020	8,000
Wholesale | Total noninvestment- grade
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	135,674	118,234
Wholesale | Noncriticized
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	117,052	110,521
Wholesale | Criticized performing
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	15,304	6,656
Wholesale | Criticized nonaccrual
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	3,318	1,057
Wholesale | U.S.
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	406,846	380,302
Wholesale | Non-U.S.
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	108,101	101,376
Wholesale | Secured by real estate
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 119,993	$ 120,418
% of investment-grade to total retained loans	75.13%	80.23%
% of total criticized to total retained loans	3.10%	1.09%
% of criticized nonaccrual to total retained loans	0.40%	0.15%
Term loans originated in 2020	$ 19,887
Term loans originated in 2019	23,914
Term loans originated in 2018	16,397
Term loans originated in 2017	13,933
Term loans originated in 2016	16,014
Term loans originated prior to 2016	28,260
Revolving loans within the revolving period	1,587
Revolving loans converted to term loans	1
Net charge-offs/(recoveries)	$ 10	$ 44
% of net charge-offs/(recoveries) to end-of-period retained loans	0.01%	0.04%
Wholesale | Secured by real estate | Current and less than 30 days past due and still accruing
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 118,894	$ 120,119
Wholesale | Secured by real estate | 30–89 days past due and still accruing
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	601	115
Wholesale | Secured by real estate | 90 or more days past due and still accruing
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	15	1
Wholesale | Secured by real estate | Investment-grade
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	90,147	96,611
Term loans originated in 2020	16,560
Term loans originated in 2019	19,575
Term loans originated in 2018	12,192
Term loans originated in 2017	11,017
Term loans originated in 2016	13,439
Term loans originated prior to 2016	16,266
Revolving loans within the revolving period	1,098
Revolving loans converted to term loans	0
Wholesale | Secured by real estate | Total noninvestment- grade
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	29,846	23,807
Term loans originated in 2020	3,327
Term loans originated in 2019	4,339
Term loans originated in 2018	4,205
Term loans originated in 2017	2,916
Term loans originated in 2016	2,575
Term loans originated prior to 2016	11,994
Revolving loans within the revolving period	489
Revolving loans converted to term loans	1
Wholesale | Secured by real estate | Noncriticized
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	26,129	22,493
Wholesale | Secured by real estate | Criticized performing
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	3,234	1,131
Wholesale | Secured by real estate | Criticized nonaccrual
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 483	$ 183
% of criticized nonaccrual to total retained loans	0.40%	0.15%
Wholesale | Secured by real estate | U.S.
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 116,990	$ 117,836
Wholesale | Secured by real estate | Non-U.S.
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	3,003	2,582
Wholesale | Commercial and industrial
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 142,709	$ 146,169
% of investment-grade to total retained loans	50.39%	55.07%
% of total criticized to total retained loans	9.05%	3.59%
% of criticized nonaccrual to total retained loans	1.35%	0.58%
Term loans originated in 2020	$ 36,271
Term loans originated in 2019	15,940
Term loans originated in 2018	8,065
Term loans originated in 2017	3,852
Term loans originated in 2016	1,529
Term loans originated prior to 2016	3,702
Revolving loans within the revolving period	73,276
Revolving loans converted to term loans	74
Net charge-offs/(recoveries)	$ 737	$ 335
% of net charge-offs/(recoveries) to end-of-period retained loans	0.52%	0.23%
Wholesale | Commercial and industrial | Current and less than 30 days past due and still accruing
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 140,100	$ 144,839
Wholesale | Commercial and industrial | 30–89 days past due and still accruing
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	658	449
Wholesale | Commercial and industrial | 90 or more days past due and still accruing
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	20	37
Wholesale | Commercial and industrial | Investment-grade
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	71,917	80,489
Term loans originated in 2020	21,211
Term loans originated in 2019	7,304
Term loans originated in 2018	2,934
Term loans originated in 2017	1,748
Term loans originated in 2016	1,032
Term loans originated prior to 2016	1,263
Revolving loans within the revolving period	36,424
Revolving loans converted to term loans	1
Wholesale | Commercial and industrial | Investment-grade | Paycheck Protection Program (PPP)
Loans and Leases Receivable Disclosure [Line Items]
Term loans originated in 2020	7,400
Wholesale | Commercial and industrial | Total noninvestment- grade
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	70,792	65,680
Term loans originated in 2020	15,060
Term loans originated in 2019	8,636
Term loans originated in 2018	5,131
Term loans originated in 2017	2,104
Term loans originated in 2016	497
Term loans originated prior to 2016	2,439
Revolving loans within the revolving period	36,852
Revolving loans converted to term loans	73
Wholesale | Commercial and industrial | Noncriticized
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	57,870	60,437
Wholesale | Commercial and industrial | Criticized performing
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	10,991	4,399
Wholesale | Commercial and industrial | Criticized nonaccrual
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	1,931	844
Wholesale | Commercial and industrial | U.S.
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	109,273	111,954
Wholesale | Commercial and industrial | Non-U.S.
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	33,436	34,215
Wholesale | Other
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 252,245	$ 215,091
% of investment-grade to total retained loans	86.11%	86.63%
% of total criticized to total retained loans	0.79%	0.54%
% of criticized nonaccrual to total retained loans	0.36%	0.01%
Term loans originated in 2020	$ 36,398
Term loans originated in 2019	12,389
Term loans originated in 2018	8,635
Term loans originated in 2017	6,756
Term loans originated in 2016	3,699
Term loans originated prior to 2016	13,231
Revolving loans within the revolving period	170,234
Revolving loans converted to term loans	903
Net charge-offs/(recoveries)	$ 52	$ 36
% of net charge-offs/(recoveries) to end-of-period retained loans	0.02%	0.02%
Wholesale | Other | Current and less than 30 days past due and still accruing
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 249,713	$ 214,641
Wholesale | Other | 30–89 days past due and still accruing
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	1,606	415
Wholesale | Other | 90 or more days past due and still accruing
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	22	5
Wholesale | Other | Investment-grade
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	217,209	186,344
Term loans originated in 2020	31,389
Term loans originated in 2019	10,169
Term loans originated in 2018	6,994
Term loans originated in 2017	6,206
Term loans originated in 2016	3,553
Term loans originated prior to 2016	12,595
Revolving loans within the revolving period	145,524
Revolving loans converted to term loans	779
Wholesale | Other | Total noninvestment- grade
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	35,036	28,747
Term loans originated in 2020	5,009
Term loans originated in 2019	2,220
Term loans originated in 2018	1,641
Term loans originated in 2017	550
Term loans originated in 2016	146
Term loans originated prior to 2016	636
Revolving loans within the revolving period	24,710
Revolving loans converted to term loans	124
Wholesale | Other | Noncriticized
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	33,053	27,591
Wholesale | Other | Criticized performing
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	1,079	1,126
Wholesale | Other | Criticized nonaccrual
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	904	30
Wholesale | Other | U.S.
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	180,583	150,512
Wholesale | Other | Non-U.S.
Loans and Leases Receivable Disclosure [Line Items]
Total retained loans	$ 71,662	$ 64,579