Loans - Wholesale Loan Portfolio, Internal Risk Ratings (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 974,260	$ 960,506	$ 945,537
Wholesale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 532,786	$ 514,947	$ 500,841
% of investment-grade to total retained loans	72.92%	73.65%
% of total criticized to total retained loans	2.79%	3.62%
% of criticized nonaccrual to total retained loans	0.39%	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	$ 528,033	$ 508,707
Wholesale | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	2,485	2,865
Wholesale | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	184	57
Wholesale | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	414,443	406,846
Wholesale | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	118,343	108,101
Wholesale | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	388,506	379,273
Wholesale | Investment-grade | Paycheck Protection Program (PPP)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	2,200	8,000
Wholesale | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	144,280	135,674
Wholesale | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	129,416	117,052
Wholesale | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	12,780	15,304
Wholesale | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	2,084	3,318
Wholesale | Secured by real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 118,167	$ 119,993
% of investment-grade to total retained loans	76.34%	75.13%
% of total criticized to total retained loans	3.64%	3.10%
% of criticized nonaccrual to total retained loans	0.32%	0.40%
Term loans originated in 2021/2020	$ 19,554	$ 22,002
Term loans originated in 2020/2019	20,613	25,897
Term loans originated in 2019/2018	23,268	18,334
Term loans originated in 2018/2017	13,830	15,402
Term loans originated in 2017/2016	11,551	17,349
Term loans originated prior to 2017/2016	27,678	19,421
Revolving loans within the revolving period	1,663	1,587
Revolving loans converted to term loans	10	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	117,563	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	150	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	79	15
Wholesale | Secured by real estate | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	115,155	116,990
Wholesale | Secured by real estate | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	3,012	3,003
Wholesale | Secured by real estate | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	90,209	90,147
Term loans originated in 2021/2020	15,893	17,004
Term loans originated in 2020/2019	16,153	19,870
Term loans originated in 2019/2018	18,216	12,448
Term loans originated in 2018/2017	9,486	11,218
Term loans originated in 2017/2016	8,240	13,611
Term loans originated prior to 2017/2016	21,072	14,898
Revolving loans within the revolving period	1,141	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	27,958	29,846
Term loans originated in 2021/2020	3,661	4,998
Term loans originated in 2020/2019	4,460	6,027
Term loans originated in 2019/2018	5,052	5,886
Term loans originated in 2018/2017	4,344	4,184
Term loans originated in 2017/2016	3,311	3,738
Term loans originated prior to 2017/2016	6,606	4,523
Revolving loans within the revolving period	522	489
Revolving loans converted to term loans	2	1
Wholesale | Secured by real estate | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	23,661	26,129
Wholesale | Secured by real estate | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	3,922	3,234
Wholesale | Secured by real estate | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 375	$ 483
% of criticized nonaccrual to total retained loans	0.32%	0.40%
Wholesale | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 133,476	$ 142,709
% of investment-grade to total retained loans	51.03%	50.39%
% of total criticized to total retained loans	6.52%	9.05%
% of criticized nonaccrual to total retained loans	0.74%	1.35%
Term loans originated in 2021/2020	$ 30,027	$ 36,721
Term loans originated in 2020/2019	15,558	16,530
Term loans originated in 2019/2018	9,736	8,420
Term loans originated in 2018/2017	4,229	4,079
Term loans originated in 2017/2016	2,429	1,645
Term loans originated prior to 2017/2016	1,888	1,964
Revolving loans within the revolving period	69,532	73,276
Revolving loans converted to term loans	77	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	131,863	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	546	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	73	20
Wholesale | Commercial and industrial | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	95,657	109,273
Wholesale | Commercial and industrial | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	37,819	33,436
Wholesale | Commercial and industrial | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	68,112	71,917
Term loans originated in 2021/2020	16,741	21,233
Term loans originated in 2020/2019	7,060	7,341
Term loans originated in 2019/2018	4,243	2,950
Term loans originated in 2018/2017	1,496	1,756
Term loans originated in 2017/2016	1,288	1,034
Term loans originated prior to 2017/2016	1,104	1,178
Revolving loans within the revolving period	36,179	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	2,000	7,400
Term loans originated in 2021/2020	1,300
Term loans originated in 2020/2019	639
Wholesale | Commercial and industrial | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	65,364	70,792
Term loans originated in 2021/2020	13,286	15,488
Term loans originated in 2020/2019	8,498	9,189
Term loans originated in 2019/2018	5,493	5,470
Term loans originated in 2018/2017	2,733	2,323
Term loans originated in 2017/2016	1,141	611
Term loans originated prior to 2017/2016	784	786
Revolving loans within the revolving period	33,353	36,852
Revolving loans converted to term loans	76	73
Wholesale | Commercial and industrial | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	56,658	57,870
Wholesale | Commercial and industrial | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	7,712	10,991
Wholesale | Commercial and industrial | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	994	1,931
Wholesale | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 281,143	$ 252,245
% of investment-grade to total retained loans	81.87%	86.11%
% of total criticized to total retained loans	0.66%	0.79%
% of criticized nonaccrual to total retained loans	0.25%	0.36%
Term loans originated in 2021/2020	$ 34,312	$ 38,238
Term loans originated in 2020/2019	23,266	13,347
Term loans originated in 2019/2018	8,567	9,115
Term loans originated in 2018/2017	4,654	7,357
Term loans originated in 2017/2016	4,497	4,264
Term loans originated prior to 2017/2016	10,504	8,787
Revolving loans within the revolving period	194,882	170,234
Revolving loans converted to term loans	461	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	278,607	249,713
Wholesale | Other | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	1,789	1,606
Wholesale | Other | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	32	22
Wholesale | Other | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	203,631	180,583
Wholesale | Other | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	77,512	71,662
Wholesale | Other | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	230,185	217,209
Term loans originated in 2021/2020	22,301	33,190
Term loans originated in 2020/2019	20,154	11,116
Term loans originated in 2019/2018	7,079	7,455
Term loans originated in 2018/2017	3,229	6,804
Term loans originated in 2017/2016	4,185	4,089
Term loans originated prior to 2017/2016	8,930	8,252
Revolving loans within the revolving period	163,875	145,524
Revolving loans converted to term loans	432	779
Wholesale | Other | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	50,958	35,036
Term loans originated in 2021/2020	12,011	5,048
Term loans originated in 2020/2019	3,112	2,231
Term loans originated in 2019/2018	1,488	1,660
Term loans originated in 2018/2017	1,425	553
Term loans originated in 2017/2016	312	175
Term loans originated prior to 2017/2016	1,574	535
Revolving loans within the revolving period	31,007	24,710
Revolving loans converted to term loans	29	124
Wholesale | Other | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	49,097	33,053
Wholesale | Other | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	1,146	1,079
Wholesale | Other | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 715	$ 904