Loans - Wholesale Loan Portfolio, Internal Risk Ratings (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 948,642	$ 960,506	$ 1,003,089
Wholesale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 514,478	$ 514,947	$ 555,289
% of investment-grade to total retained loans	73.83%	73.65%
% of total criticized to total retained loans	3.68%	3.62%
% of criticized nonaccrual to total retained loans	0.59%	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	$ 508,171	$ 508,707
Wholesale | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	3,061	2,865
Wholesale | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	231	57
Wholesale | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	379,827	379,273
Wholesale | Investment-grade | Paycheck Protection Program (PPP)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans originated in 2021/2020	1,200	8,000
Term loans originated in 2020/2019	7,700
Wholesale | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	134,651	135,674
Wholesale | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	115,743	117,052
Wholesale | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	15,893	15,304
Wholesale | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	3,015	3,318
Wholesale | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	403,032	406,846
Wholesale | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	111,446	108,101
Wholesale | Secured by real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 118,538	$ 119,993
% of investment-grade to total retained loans	74.53%	75.13%
% of total criticized to total retained loans	3.59%	3.10%
% of criticized nonaccrual to total retained loans	0.42%	0.40%
Term loans originated in 2021/2020	$ 3,589	$ 19,887
Term loans originated in 2020/2019	19,706	23,914
Term loans originated in 2019/2018	23,554	16,397
Term loans originated in 2018/2017	15,400	13,933
Term loans originated in 2017/2016	13,002	16,014
Term loans originated prior to 2017/2016	41,705	28,260
Revolving loans within the revolving period	1,581	1,587
Revolving loans converted to term loans	1	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	117,559	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	462	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	15	15
Wholesale | Secured by real estate | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	88,351	90,147
Term loans originated in 2021/2020	2,966	16,560
Term loans originated in 2020/2019	16,303	19,575
Term loans originated in 2019/2018	19,118	12,192
Term loans originated in 2018/2017	11,307	11,017
Term loans originated in 2017/2016	10,192	13,439
Term loans originated prior to 2017/2016	27,314	16,266
Revolving loans within the revolving period	1,151	1,098
Revolving loans converted to term loans	0	0
Wholesale | Secured by real estate | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	30,187	29,846
Term loans originated in 2021/2020	623	3,327
Term loans originated in 2020/2019	3,403	4,339
Term loans originated in 2019/2018	4,436	4,205
Term loans originated in 2018/2017	4,093	2,916
Term loans originated in 2017/2016	2,810	2,575
Term loans originated prior to 2017/2016	14,391	11,994
Revolving loans within the revolving period	430	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	25,929	26,129
Wholesale | Secured by real estate | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	3,756	3,234
Wholesale | Secured by real estate | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 502	$ 483
% of criticized nonaccrual to total retained loans	0.42%	0.40%
Wholesale | Secured by real estate | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 115,451	$ 116,990
Wholesale | Secured by real estate | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	3,087	3,003
Wholesale | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 139,620	$ 142,709
% of investment-grade to total retained loans	51.89%	50.39%
% of total criticized to total retained loans	9.14%	9.05%
% of criticized nonaccrual to total retained loans	1.25%	1.35%
Term loans originated in 2021/2020	$ 12,379	$ 36,271
Term loans originated in 2020/2019	26,714	15,940
Term loans originated in 2019/2018	13,669	8,065
Term loans originated in 2018/2017	7,115	3,852
Term loans originated in 2017/2016	3,362	1,529
Term loans originated prior to 2017/2016	4,606	3,702
Revolving loans within the revolving period	71,632	73,276
Revolving loans converted to term loans	143	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	136,980	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	830	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	58	20
Wholesale | Commercial and industrial | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	72,453	71,917
Term loans originated in 2021/2020	8,403	21,211
Term loans originated in 2020/2019	14,857	7,304
Term loans originated in 2019/2018	6,587	2,934
Term loans originated in 2018/2017	2,474	1,748
Term loans originated in 2017/2016	1,664	1,032
Term loans originated prior to 2017/2016	1,861	1,263
Revolving loans within the revolving period	36,537	36,424
Revolving loans converted to term loans	70	1
Wholesale | Commercial and industrial | Investment-grade | Paycheck Protection Program (PPP)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term loans originated in 2021/2020	1,200	7,400
Term loans originated in 2020/2019	7,100
Wholesale | Commercial and industrial | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	67,167	70,792
Term loans originated in 2021/2020	3,976	15,060
Term loans originated in 2020/2019	11,857	8,636
Term loans originated in 2019/2018	7,082	5,131
Term loans originated in 2018/2017	4,641	2,104
Term loans originated in 2017/2016	1,698	497
Term loans originated prior to 2017/2016	2,745	2,439
Revolving loans within the revolving period	35,095	36,852
Revolving loans converted to term loans	73	73
Wholesale | Commercial and industrial | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	54,410	57,870
Wholesale | Commercial and industrial | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	11,005	10,991
Wholesale | Commercial and industrial | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	1,752	1,931
Wholesale | Commercial and industrial | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	106,309	109,273
Wholesale | Commercial and industrial | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	33,311	33,436
Wholesale | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 256,320	$ 252,245
% of investment-grade to total retained loans	85.45%	86.11%
% of total criticized to total retained loans	0.74%	0.79%
% of criticized nonaccrual to total retained loans	0.30%	0.36%
Term loans originated in 2021/2020	$ 11,983	$ 36,398
Term loans originated in 2020/2019	29,868	12,389
Term loans originated in 2019/2018	10,368	8,635
Term loans originated in 2018/2017	6,673	6,756
Term loans originated in 2017/2016	6,359	3,699
Term loans originated prior to 2017/2016	17,962	13,231
Revolving loans within the revolving period	172,380	170,234
Revolving loans converted to term loans	727	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	253,632	249,713
Wholesale | Other | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	1,769	1,606
Wholesale | Other | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	158	22
Wholesale | Other | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	219,023	217,209
Term loans originated in 2021/2020	8,483	31,389
Term loans originated in 2020/2019	25,689	10,169
Term loans originated in 2019/2018	8,177	6,994
Term loans originated in 2018/2017	5,052	6,206
Term loans originated in 2017/2016	5,874	3,553
Term loans originated prior to 2017/2016	16,897	12,595
Revolving loans within the revolving period	148,248	145,524
Revolving loans converted to term loans	603	779
Wholesale | Other | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	37,297	35,036
Term loans originated in 2021/2020	3,500	5,009
Term loans originated in 2020/2019	4,179	2,220
Term loans originated in 2019/2018	2,191	1,641
Term loans originated in 2018/2017	1,621	550
Term loans originated in 2017/2016	485	146
Term loans originated prior to 2017/2016	1,065	636
Revolving loans within the revolving period	24,132	24,710
Revolving loans converted to term loans	124	124
Wholesale | Other | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	35,404	33,053
Wholesale | Other | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	1,132	1,079
Wholesale | Other | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	761	904
Wholesale | Other | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	181,272	180,583
Wholesale | Other | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total retained loans	$ 75,048	$ 71,662