Loans - Wholesale Loan Portfolio, Internal Risk Ratings (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 963,665	$ 960,506	$ 965,448
Wholesale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 524,855	$ 514,947	$ 516,787
% of investment-grade to total retained loans	73.73%	73.65%
% of total criticized to total retained loans	3.07%	3.62%
% of criticized nonaccrual to total retained loans	0.51%	0.64%
Wholesale | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 519,721	$ 508,707
Wholesale | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	2,330	2,865
Wholesale | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	106	57
Wholesale | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	387,000	379,273
Wholesale | Investment-grade | Paycheck Protection Program (PPP)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	5,800	8,000
Wholesale | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	137,855	135,674
Wholesale | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	121,753	117,052
Wholesale | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	13,404	15,304
Wholesale | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	2,698	3,318
Wholesale | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	406,535	406,846
Wholesale | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	118,320	108,101
Wholesale | Secured by real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 118,023	$ 119,993
% of investment-grade to total retained loans	75.08%	75.13%
% of total criticized to total retained loans	3.87%	3.10%
% of criticized nonaccrual to total retained loans	0.41%	0.40%
Term loans originated in 2021/2020	$ 10,616	$ 19,887
Term loans originated in 2020/2019	19,293	23,914
Term loans originated in 2019/2018	22,624	16,397
Term loans originated in 2018/2017	14,005	13,933
Term loans originated in 2017/2016	11,521	16,014
Term loans originated prior to 2017/2016	38,273	28,260
Revolving loans within the revolving period	1,682	1,587
Revolving loans converted to term loans	9	1
Wholesale | Secured by real estate | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	117,315	118,894
Wholesale | Secured by real estate | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	200	601
Wholesale | Secured by real estate | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	19	15
Wholesale | Secured by real estate | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	88,617	90,147
Term loans originated in 2021/2020	9,394	16,560
Term loans originated in 2020/2019	15,951	19,575
Term loans originated in 2019/2018	18,482	12,192
Term loans originated in 2018/2017	10,350	11,017
Term loans originated in 2017/2016	8,962	13,439
Term loans originated prior to 2017/2016	24,226	16,266
Revolving loans within the revolving period	1,244	1,098
Revolving loans converted to term loans	8	0
Wholesale | Secured by real estate | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	29,406	29,846
Term loans originated in 2021/2020	1,222	3,327
Term loans originated in 2020/2019	3,342	4,339
Term loans originated in 2019/2018	4,142	4,205
Term loans originated in 2018/2017	3,655	2,916
Term loans originated in 2017/2016	2,559	2,575
Term loans originated prior to 2017/2016	14,047	11,994
Revolving loans within the revolving period	438	489
Revolving loans converted to term loans	1	1
Wholesale | Secured by real estate | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	24,840	26,129
Wholesale | Secured by real estate | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	4,077	3,234
Wholesale | Secured by real estate | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 489	$ 483
% of criticized nonaccrual to total retained loans	0.41%	0.40%
Wholesale | Secured by real estate | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 115,043	$ 116,990
Wholesale | Secured by real estate | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	2,980	3,003
Wholesale | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 134,212	$ 142,709
% of investment-grade to total retained loans	53.28%	50.39%
% of total criticized to total retained loans	7.22%	9.05%
% of criticized nonaccrual to total retained loans	1.05%	1.35%
Term loans originated in 2021/2020	$ 22,826	$ 36,271
Term loans originated in 2020/2019	19,772	15,940
Term loans originated in 2019/2018	11,091	8,065
Term loans originated in 2018/2017	5,803	3,852
Term loans originated in 2017/2016	3,109	1,529
Term loans originated prior to 2017/2016	3,768	3,702
Revolving loans within the revolving period	67,763	73,276
Revolving loans converted to term loans	80	74
Wholesale | Commercial and industrial | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	131,948	140,100
Wholesale | Commercial and industrial | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	822	658
Wholesale | Commercial and industrial | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	29	20
Wholesale | Commercial and industrial | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	71,509	71,917
Term loans originated in 2021/2020	15,656	21,211
Term loans originated in 2020/2019	10,269	7,304
Term loans originated in 2019/2018	4,965	2,934
Term loans originated in 2018/2017	2,266	1,748
Term loans originated in 2017/2016	1,669	1,032
Term loans originated prior to 2017/2016	1,413	1,263
Revolving loans within the revolving period	35,270	36,424
Revolving loans converted to term loans	1	1
Wholesale | Commercial and industrial | Investment-grade | Paycheck Protection Program (PPP)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	5,300	7,400
Term loans originated in 2021/2020	1,400
Term loans originated in 2020/2019	3,900
Wholesale | Commercial and industrial | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	62,703	70,792
Term loans originated in 2021/2020	7,170	15,060
Term loans originated in 2020/2019	9,503	8,636
Term loans originated in 2019/2018	6,126	5,131
Term loans originated in 2018/2017	3,537	2,104
Term loans originated in 2017/2016	1,440	497
Term loans originated prior to 2017/2016	2,355	2,439
Revolving loans within the revolving period	32,493	36,852
Revolving loans converted to term loans	79	73
Wholesale | Commercial and industrial | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	53,017	57,870
Wholesale | Commercial and industrial | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	8,273	10,991
Wholesale | Commercial and industrial | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	1,413	1,931
Wholesale | Commercial and industrial | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	98,570	109,273
Wholesale | Commercial and industrial | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	35,642	33,436
Wholesale | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 272,620	$ 252,245
% of investment-grade to total retained loans	83.22%	86.11%
% of total criticized to total retained loans	0.68%	0.79%
% of criticized nonaccrual to total retained loans	0.29%	0.36%
Term loans originated in 2021/2020	$ 26,043	$ 36,398
Term loans originated in 2020/2019	23,907	12,389
Term loans originated in 2019/2018	9,521	8,635
Term loans originated in 2018/2017	5,253	6,756
Term loans originated in 2017/2016	5,600	3,699
Term loans originated prior to 2017/2016	14,641	13,231
Revolving loans within the revolving period	187,069	170,234
Revolving loans converted to term loans	586	903
Wholesale | Other | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	270,458	249,713
Wholesale | Other | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	1,308	1,606
Wholesale | Other | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	58	22
Wholesale | Other | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	226,874	217,209
Term loans originated in 2021/2020	16,199	31,389
Term loans originated in 2020/2019	20,538	10,169
Term loans originated in 2019/2018	7,530	6,994
Term loans originated in 2018/2017	3,913	6,206
Term loans originated in 2017/2016	5,159	3,553
Term loans originated prior to 2017/2016	13,750	12,595
Revolving loans within the revolving period	159,224	145,524
Revolving loans converted to term loans	561	779
Wholesale | Other | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	45,746	35,036
Term loans originated in 2021/2020	9,844	5,009
Term loans originated in 2020/2019	3,369	2,220
Term loans originated in 2019/2018	1,991	1,641
Term loans originated in 2018/2017	1,340	550
Term loans originated in 2017/2016	441	146
Term loans originated prior to 2017/2016	891	636
Revolving loans within the revolving period	27,845	24,710
Revolving loans converted to term loans	25	124
Wholesale | Other | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	43,896	33,053
Wholesale | Other | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	1,054	1,079
Wholesale | Other | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	796	904
Wholesale | Other | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	192,922	180,583
Wholesale | Other | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 79,698	$ 71,662