Loans - Wholesale Loan Portfolio - By Class of Receivable (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 940,440	$ 924,838	$ 899,576
Wholesale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 420,632	$ 402,898	$ 394,426
% of total criticized exposure to total retained loans	1.24%	1.71%
% of criticized nonaccrual to total retained loans	0.27%	0.43%
Wholesale | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 417,748	$ 399,640
Wholesale | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,665	1,383
Wholesale | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	63	141
Wholesale | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	103,678	95,379
Wholesale | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	316,954	307,519
Wholesale | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	322,105	311,681
Wholesale | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	98,527	91,217
Wholesale | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	93,309	84,321
Wholesale | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,062	5,162
Wholesale | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,156	1,734
Wholesale | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 124,426	$ 119,969
% of total criticized exposure to total retained loans	3.17%	4.45%
% of criticized nonaccrual to total retained loans	0.65%	1.13%
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	$ 123,396	$ 118,288
Wholesale | Commercial and industrial | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	188	216
Wholesale | Commercial and industrial | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	29	108
Wholesale | Commercial and industrial | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	30,725	28,470
Wholesale | Commercial and industrial | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	93,701	91,499
Wholesale | Commercial and industrial | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	70,285	68,071
Wholesale | Commercial and industrial | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	54,141	51,898
Wholesale | Commercial and industrial | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	50,197	46,558
Wholesale | Commercial and industrial | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,131	3,983
Wholesale | Commercial and industrial | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	813	1,357
Wholesale | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 113,340	$ 113,648
% of total criticized exposure to total retained loans	0.62%	0.74%
% of criticized nonaccrual to total retained loans	0.12%	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	$ 112,506	$ 113,258
Wholesale | Real estate | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	675	242
Wholesale | Real estate | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	21	12
Wholesale | Real estate | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2,668	3,101
Wholesale | Real estate | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	110,672	110,547
Wholesale | Real estate | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	98,684	98,467
Wholesale | Real estate | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	14,656	15,181
Wholesale | Real estate | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	13,952	14,335
Wholesale | Real estate | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	566	710
Wholesale | Real estate | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	138	136
Wholesale | Financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 44,628	$ 40,074
% of total criticized exposure to total retained loans	0.30%	0.53%
% of criticized nonaccrual to total retained loans	0.00%	0.00%
Wholesale | Financial institutions | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 44,607	$ 40,042
Wholesale | Financial institutions | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	11	15
Wholesale | Financial institutions | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	8	15
Wholesale | Financial institutions | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	17,506	16,790
Wholesale | Financial institutions | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	27,122	23,284
Wholesale | Financial institutions | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	29,585	26,791
Wholesale | Financial institutions | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	15,043	13,283
Wholesale | Financial institutions | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	14,907	13,071
Wholesale | Financial institutions | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	134	210
Wholesale | Financial institutions | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2	2
Wholesale | Government agencies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 15,498	$ 15,509
% of total criticized exposure to total retained loans	0.00%	0.00%
% of criticized nonaccrual to total retained loans	0.00%	0.00%
Wholesale | Government agencies | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 15,491	$ 15,493
Wholesale | Government agencies | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3	12
Wholesale | Government agencies | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4	4
Wholesale | Government agencies | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2,966	2,906
Wholesale | Government agencies | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	12,532	12,603
Wholesale | Government agencies | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	15,332	15,140
Wholesale | Government agencies | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	166	369
Wholesale | Government agencies | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	166	369
Wholesale | Government agencies | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	0	0
Wholesale | Government 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	$ 122,740	$ 113,698
% of total criticized exposure to total retained loans	0.35%	0.44%
% of criticized nonaccrual to total retained loans	0.17%	0.21%
Wholesale | Other | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 121,748	$ 112,559
Wholesale | Other | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	788	898
Wholesale | Other | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1	2
Wholesale | Other | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	49,813	44,112
Wholesale | Other | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	72,927	69,586
Wholesale | Other | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	108,219	103,212
Wholesale | Other | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	14,521	10,486
Wholesale | Other | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	14,087	9,988
Wholesale | Other | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	231	259
Wholesale | Other | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 203	$ 239