Cash Instruments - Cash Instruments by Level (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	$ 424,989	$ 336,161
Financial instruments sold, but not yet purchased	(116,423)	(108,897)
Cash Instruments Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	370,885	287,379
Investments in funds at NAV	4,232	3,936
Total cash instrument assets	375,117	291,315
Cash Instruments Assets [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	238,662	170,441
Cash Instruments Assets [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	113,837	99,711
Cash Instruments Assets [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	18,386	17,227
Cash Instruments Assets [Member] | Money Market Instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	3,715	2,635
Cash Instruments Assets [Member] | Money Market Instruments [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	1,545	1,489
Cash Instruments Assets [Member] | Money Market Instruments [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	2,170	1,146
Cash Instruments Assets [Member] | U.S. Government and Agency Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	131,500	110,616
Cash Instruments Assets [Member] | U.S. Government and Agency Obligations [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	100,276	82,264
Cash Instruments Assets [Member] | U.S. Government and Agency Obligations [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	31,204	28,327
Cash Instruments Assets [Member] | U.S. Government and Agency Obligations [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	20	25
Cash Instruments Assets [Member] | Non-U.S. Government and Agency Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	55,657	43,607
Cash Instruments Assets [Member] | Non-U.S. Government and Agency Obligations [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	42,386	33,231
Cash Instruments Assets [Member] | Non-U.S. Government and Agency Obligations [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	13,186	10,366
Cash Instruments Assets [Member] | Non-U.S. Government and Agency Obligations [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	85	10
Cash Instruments Assets [Member] | Loans and Securities Backed by Commercial Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	3,713	3,369
Cash Instruments Assets [Member] | Loans and Securities Backed by Commercial Real Estate [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	2,891	2,350
Cash Instruments Assets [Member] | Loans and Securities Backed by Commercial Real Estate [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	822	1,019
Cash Instruments Assets [Member] | Loans and Securities Backed by Residential Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	14,717	12,949
Cash Instruments Assets [Member] | Loans and Securities Backed by Residential Real Estate [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	14,254	12,286
Cash Instruments Assets [Member] | Loans and Securities Backed by Residential Real Estate [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	463	663
Cash Instruments Assets [Member] | Corporate debt instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	39,042	31,207
Cash Instruments Assets [Member] | Corporate debt instruments [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	1,228	468
Cash Instruments Assets [Member] | Corporate debt instruments [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	33,026	26,515
Cash Instruments Assets [Member] | Corporate debt instruments [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	4,788	4,224
Cash Instruments Assets [Member] | State and Municipal Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	1,233	1,233
Cash Instruments Assets [Member] | State and Municipal Obligations [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	1,194	1,210
Cash Instruments Assets [Member] | State and Municipal Obligations [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	39	23
Cash Instruments Assets [Member] | Other debt obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	1,708	1,864
Cash Instruments Assets [Member] | Other debt obligations [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	1,067	1,326
Cash Instruments Assets [Member] | Other debt obligations [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	641	538
Cash Instruments Assets [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	116,047	76,170
Cash Instruments Assets [Member] | Equity Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	93,227	52,989
Cash Instruments Assets [Member] | Equity Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	11,292	12,456
Cash Instruments Assets [Member] | Equity Securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	11,528	10,725
Cash Instruments Assets [Member] | Commodities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	3,553	3,729
Cash Instruments Assets [Member] | Commodities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	3,553	3,729
Cash Instruments Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(70,702)	(66,303)
Cash Instruments Liabilities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(59,531)	(54,090)
Cash Instruments Liabilities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(10,931)	(12,164)
Cash Instruments Liabilities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(240)	(49)
Cash Instruments Liabilities [Member] | U.S. Government and Agency Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(12,374)	(5,080)
Cash Instruments Liabilities [Member] | U.S. Government and Agency Obligations [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(12,326)	(5,067)
Cash Instruments Liabilities [Member] | U.S. Government and Agency Obligations [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(48)	(13)
Cash Instruments Liabilities [Member] | Non-U.S. Government and Agency Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(23,438)	(25,347)
Cash Instruments Liabilities [Member] | Non-U.S. Government and Agency Obligations [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(21,350)	(23,872)
Cash Instruments Liabilities [Member] | Non-U.S. Government and Agency Obligations [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(2,087)	(1,475)
Cash Instruments Liabilities [Member] | Non-U.S. Government and Agency Obligations [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(1)
Cash Instruments Liabilities [Member] | Loans and Securities Backed by Commercial Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(28)
Cash Instruments Liabilities [Member] | Loans and Securities Backed by Commercial Real Estate [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(27)
Cash Instruments Liabilities [Member] | Loans and Securities Backed by Commercial Real Estate [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(1)
Cash Instruments Liabilities [Member] | Loans and Securities Backed by Residential Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(7)	(1)
Cash Instruments Liabilities [Member] | Loans and Securities Backed by Residential Real Estate [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(6)	(1)
Cash Instruments Liabilities [Member] | Loans and Securities Backed by Residential Real Estate [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(1)
Cash Instruments Liabilities [Member] | Corporate debt instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(8,660)	(10,411)
Cash Instruments Liabilities [Member] | Corporate debt instruments [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(59)	(4)
Cash Instruments Liabilities [Member] | Corporate debt instruments [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(8,381)	(10,376)
Cash Instruments Liabilities [Member] | Corporate debt instruments [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(220)	(31)
Cash Instruments Liabilities [Member] | State and Municipal Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(2)
Cash Instruments Liabilities [Member] | State and Municipal Obligations [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(2)
Cash Instruments Liabilities [Member] | Other debt obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased		(1)
Cash Instruments Liabilities [Member] | Other debt obligations [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased		(1)
Cash Instruments Liabilities [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(26,193)	(25,463)
Cash Instruments Liabilities [Member] | Equity Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(25,796)	(25,147)
Cash Instruments Liabilities [Member] | Equity Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	(380)	(298)
Cash Instruments Liabilities [Member] | Equity Securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments sold, but not yet purchased	$ (17)	$ (18)