Loans - Wholesale Loan Portfolio - By Class of Receivable (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 947,651	$ 924,838	$ 909,182
Wholesale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 423,837	$ 402,898	$ 398,569
% of total criticized exposure to total retained loans	1.27%	1.71%
% of criticized nonaccrual to total retained loans	0.23%	0.43%
Wholesale | Current and less than 30 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 421,364	$ 399,640
Wholesale | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,426	1,383
Wholesale | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	53	141
Wholesale | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	102,927	95,379
Wholesale | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	320,910	307,519
Wholesale | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	324,343	311,681
Wholesale | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	99,494	91,217
Wholesale | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	94,114	84,321
Wholesale | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	4,386	5,162
Wholesale | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	994	1,734
Wholesale | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 122,851	$ 119,969
% of total criticized exposure to total retained loans	3.36%	4.45%
% of criticized nonaccrual to total retained loans	0.57%	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	$ 121,913	$ 118,288
Wholesale | Commercial and industrial | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	211	216
Wholesale | Commercial and industrial | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	31	108
Wholesale | Commercial and industrial | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	30,435	28,470
Wholesale | Commercial and industrial | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	92,416	91,499
Wholesale | Commercial and industrial | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	66,968	68,071
Wholesale | Commercial and industrial | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	55,883	51,898
Wholesale | Commercial and industrial | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	51,758	46,558
Wholesale | Commercial and industrial | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3,429	3,983
Wholesale | Commercial and industrial | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	696	1,357
Wholesale | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 115,296	$ 113,648
% of total criticized exposure to total retained loans	0.64%	0.74%
% of criticized nonaccrual to total retained loans	0.11%	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	$ 115,098	$ 113,258
Wholesale | Real estate | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	52	242
Wholesale | Real estate | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	16	12
Wholesale | Real estate | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2,741	3,101
Wholesale | Real estate | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	112,555	110,547
Wholesale | Real estate | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	100,036	98,467
Wholesale | Real estate | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	15,260	15,181
Wholesale | Real estate | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	14,526	14,335
Wholesale | Real estate | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	604	710
Wholesale | Real estate | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	130	136
Wholesale | Financial institutions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 45,712	$ 40,074
% of total criticized exposure to total retained loans	0.32%	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	$ 45,671	$ 40,042
Wholesale | Financial institutions | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	38	15
Wholesale | Financial institutions | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1	15
Wholesale | Financial institutions | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	17,748	16,790
Wholesale | Financial institutions | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	27,964	23,284
Wholesale | Financial institutions | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	31,194	26,791
Wholesale | Financial institutions | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	14,518	13,283
Wholesale | Financial institutions | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	14,374	13,071
Wholesale | Financial institutions | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	142	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	$ 14,603	$ 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	$ 14,585	$ 15,493
Wholesale | Government agencies | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	15	12
Wholesale | Government agencies | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	3	4
Wholesale | Government agencies | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2,973	2,906
Wholesale | Government agencies | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	11,630	12,603
Wholesale | Government agencies | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	14,435	15,140
Wholesale | Government agencies | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	168	369
Wholesale | Government agencies | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	168	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	$ 125,375	$ 113,698
% of total criticized exposure to total retained loans	0.30%	0.44%
% of criticized nonaccrual to total retained loans	0.13%	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	$ 124,097	$ 112,559
Wholesale | Other | 30–89 days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	1,110	898
Wholesale | Other | 90 or more days past due and still accruing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	2	2
Wholesale | Other | Total non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	49,030	44,112
Wholesale | Other | Total U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	76,345	69,586
Wholesale | Other | Investment-grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	111,710	103,212
Wholesale | Other | Total noninvestment- grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	13,665	10,486
Wholesale | Other | Noncriticized
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	13,288	9,988
Wholesale | Other | Criticized performing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	211	259
Wholesale | Other | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 166	$ 239