Loans - Wholesale Loan Portfolio - By Class of Receivable (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 943,841	$ 969,415	$ 925,611
Wholesale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 433,611	$ 439,162	$ 412,020
% of total criticized exposure to total retained loans	1.55%	1.33%
% of criticized nonaccrual to total retained loans	0.36%	0.26%
Wholesale | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 430,006	$ 436,916
Wholesale | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,995	908
Wholesale | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	40	188
Wholesale | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	103,928	102,646
Wholesale | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	329,683	336,516
Wholesale | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	332,514	339,729
Wholesale | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	101,097	99,433
Wholesale | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	94,389	93,591
Wholesale | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	5,138	4,692
Wholesale | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,570	1,150
Wholesale | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 130,540	$ 129,806
% of total criticized exposure to total retained loans	3.92%	3.54%
% of criticized nonaccrual to total retained loans	0.85%	0.66%
Wholesale | Commercial and industrial | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 129,112	$ 128,678
Wholesale | Commercial and industrial | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	295	109
Wholesale | Commercial and industrial | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	27	168
Wholesale | Commercial and industrial | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	31,754	29,572
Wholesale | Commercial and industrial | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	98,786	100,234
Wholesale | Commercial and industrial | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	71,503	73,497
Wholesale | Commercial and industrial | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	59,037	56,309
Wholesale | Commercial and industrial | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	53,916	51,720
Wholesale | Commercial and industrial | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,015	3,738
Wholesale | Commercial and industrial | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,106	851
Wholesale | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 116,173	$ 115,737
% of total criticized exposure to total retained loans	0.79%	0.65%
% of criticized nonaccrual to total retained loans	0.10%	0.12%
Wholesale | Real estate | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 115,889	$ 115,533
Wholesale | Real estate | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	170	67
Wholesale | Real estate | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3	3
Wholesale | Real estate | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,422	2,967
Wholesale | Real estate | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	112,751	112,770
Wholesale | Real estate | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	99,755	100,107
Wholesale | Real estate | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	16,418	15,630
Wholesale | Real estate | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	15,499	14,876
Wholesale | Real estate | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	808	620
Wholesale | Real estate | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	111	134
Wholesale | Financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 47,277	$ 47,648
% of total criticized exposure to total retained loans	0.19%	0.32%
% of criticized nonaccrual to total retained loans	0.04%	0.01%
Wholesale | Financial institutions | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 47,140	$ 47,622
Wholesale | Financial institutions | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	118	12
Wholesale | Financial institutions | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	0	10
Wholesale | Financial institutions | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	18,796	18,524
Wholesale | Financial institutions | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	28,481	29,124
Wholesale | Financial institutions | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	31,909	32,178
Wholesale | Financial institutions | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	15,368	15,470
Wholesale | Financial institutions | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	15,277	15,316
Wholesale | Financial institutions | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	72	150
Wholesale | Financial institutions | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	19	4
Wholesale | Governments & Agencies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 13,600	$ 14,187
% of total criticized exposure to total retained loans	0.01%	0.01%
% of criticized nonaccrual to total retained loans	0.00%	0.00%
Wholesale | Governments & Agencies | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 13,590	$ 14,165
Wholesale | Governments & Agencies | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3	18
Wholesale | Governments & Agencies | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	7	4
Wholesale | Governments & Agencies | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,121	3,150
Wholesale | Governments & Agencies | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	10,479	11,037
Wholesale | Governments & Agencies | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	13,299	13,984
Wholesale | Governments & Agencies | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	301	203
Wholesale | Governments & Agencies | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	299	201
Wholesale | Governments & Agencies | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2	2
Wholesale | Governments & Agencies | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	0	0
Wholesale | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 126,021	$ 131,784
% of total criticized exposure to total retained loans	0.46%	0.26%
% of criticized nonaccrual to total retained loans	0.27%	0.12%
Wholesale | Other | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 124,275	$ 130,918
Wholesale | Other | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,409	702
Wholesale | Other | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3	3
Wholesale | Other | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	46,835	48,433
Wholesale | Other | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	79,186	83,351
Wholesale | Other | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	116,048	119,963
Wholesale | Other | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	9,973	11,821
Wholesale | Other | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	9,398	11,478
Wholesale | Other | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	241	182
Wholesale | Other | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 334	$ 161