Loans - Wholesale Loan Portfolio - By Class of Receivable (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 947,728	$ 969,415	$ 940,440
Wholesale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 438,468	$ 439,162	$ 420,632
% of total criticized exposure to total retained loans	1.43%	1.33%
% of criticized nonaccrual to total retained loans	0.28%	0.26%
Wholesale | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 435,722	$ 436,916
Wholesale | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,390	908
Wholesale | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	118	188
Wholesale | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	101,160	102,646
Wholesale | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	337,308	336,516
Wholesale | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	337,188	339,729
Wholesale | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	101,280	99,433
Wholesale | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	95,014	93,591
Wholesale | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	5,028	4,692
Wholesale | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,238	1,150
Wholesale | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 126,540	$ 129,806
% of total criticized exposure to total retained loans	3.49%	3.54%
% of criticized nonaccrual to total retained loans	0.74%	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	$ 125,003	$ 128,678
Wholesale | Commercial and industrial | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	493	109
Wholesale | Commercial and industrial | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	111	168
Wholesale | Commercial and industrial | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	31,054	29,572
Wholesale | Commercial and industrial | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	95,486	100,234
Wholesale | Commercial and industrial | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	67,490	73,497
Wholesale | Commercial and industrial | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	59,050	56,309
Wholesale | Commercial and industrial | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	54,639	51,720
Wholesale | Commercial and industrial | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,478	3,738
Wholesale | Commercial and industrial | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	933	851
Wholesale | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 115,603	$ 115,737
% of total criticized exposure to total retained loans	0.78%	0.65%
% of criticized nonaccrual to total retained loans	0.08%	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	$ 115,409	$ 115,533
Wholesale | Real estate | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	99	67
Wholesale | Real estate | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4	3
Wholesale | Real estate | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,248	2,967
Wholesale | Real estate | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	112,355	112,770
Wholesale | Real estate | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	100,115	100,107
Wholesale | Real estate | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	15,488	15,630
Wholesale | Real estate | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	14,582	14,876
Wholesale | Real estate | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	815	620
Wholesale | Real estate | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	91	134
Wholesale | Financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 51,419	$ 47,648
% of total criticized exposure to total retained loans	0.40%	0.32%
% of criticized nonaccrual to total retained loans	0.02%	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	$ 51,377	$ 47,622
Wholesale | Financial institutions | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	31	12
Wholesale | Financial institutions | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1	10
Wholesale | Financial institutions | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	16,632	18,524
Wholesale | Financial institutions | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	34,787	29,124
Wholesale | Financial institutions | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	36,432	32,178
Wholesale | Financial institutions | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	14,987	15,470
Wholesale | Financial institutions | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	14,779	15,316
Wholesale | Financial institutions | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	198	150
Wholesale | Financial institutions | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	10	4
Wholesale | Governments & Agencies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 13,692	$ 14,187
% of total criticized exposure to total retained loans	0.02%	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	$ 13,687	$ 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	2	4
Wholesale | Governments & Agencies | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2,753	3,150
Wholesale | Governments & Agencies | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	10,939	11,037
Wholesale | Governments & Agencies | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	13,431	13,984
Wholesale | Governments & Agencies | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	261	203
Wholesale | Governments & Agencies | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	258	201
Wholesale | Governments & Agencies | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3	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	$ 131,214	$ 131,784
% of total criticized exposure to total retained loans	0.56%	0.26%
% of criticized nonaccrual to total retained loans	0.16%	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	$ 130,246	$ 130,918
Wholesale | Other | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	764	702
Wholesale | Other | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	0	3
Wholesale | Other | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	47,473	48,433
Wholesale | Other | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	83,741	83,351
Wholesale | Other | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	119,720	119,963
Wholesale | Other | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	11,494	11,821
Wholesale | Other | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	10,756	11,478
Wholesale | Other | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	534	182
Wholesale | Other | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 204	$ 161