Trading Cash Instruments - Cash Instruments by Level (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Trading Cash Instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Trading Assets	$ 300,900	$ 310,080
Trading cash instruments assets | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	199,295	222,413
Trading cash instruments assets | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	100,371	86,425
Trading cash instruments assets | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	1,234	1,242
Trading cash instruments assets | U.S. Government and Agency Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	139,346	142,935
Trading cash instruments assets | U.S. Government and Agency Obligations [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	89,564	108,200
Trading cash instruments assets | U.S. Government and Agency Obligations [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	49,771	34,714
Trading cash instruments assets | U.S. Government and Agency Obligations [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	11	21
Trading cash instruments assets | Non-U.S. Government and Agency Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	47,434	44,839
Trading cash instruments assets | Non-U.S. Government and Agency Obligations [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	37,925	33,709
Trading cash instruments assets | Non-U.S. Government and Agency Obligations [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	9,493	11,108
Trading cash instruments assets | Non-U.S. Government and Agency Obligations [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	16	22
Trading cash instruments assets | Loans and Securities Backed by Commercial Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	2,541	2,222
Trading cash instruments assets | 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]
Trading Cash Instruments Assets at Fair Value	2,411	2,031
Trading cash instruments assets | 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]
Trading Cash Instruments Assets at Fair Value	130	191
Trading cash instruments assets | Loans and Securities Backed by Residential Real Estate [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	7,157	6,025
Trading cash instruments assets | 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]
Trading Cash Instruments Assets at Fair Value	6,906	5,794
Trading cash instruments assets | 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]
Trading Cash Instruments Assets at Fair Value	251	231
Trading cash instruments assets | Corporate debt instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	26,206	28,773
Trading cash instruments assets | Corporate debt instruments [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	683	1,313
Trading cash instruments assets | Corporate debt instruments [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	24,804	26,768
Trading cash instruments assets | Corporate debt instruments [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	719	692
Trading cash instruments assets | State and Municipal Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	347	680
Trading cash instruments assets | State and Municipal Obligations [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	347	680
Trading cash instruments assets | Other debt obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	3,568	1,493
Trading cash instruments assets | Other debt obligations [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	328	409
Trading cash instruments assets | Other debt obligations [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	3,206	1,074
Trading cash instruments assets | Other debt obligations [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	34	10
Trading cash instruments assets | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	72,059	79,346
Trading cash instruments assets | Equity Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	70,795	78,782
Trading cash instruments assets | Equity Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	1,191	489
Trading cash instruments assets | Equity Securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	73	75
Trading cash instruments assets | Commodities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	2,242	3,767
Trading cash instruments assets | Commodities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Assets at Fair Value	2,242	3,767
Cash Instruments Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Liabilities at Fair Value	(74,319)	(65,033)
Cash Instruments Liabilities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Liabilities at Fair Value	(63,068)	(54,761)
Cash Instruments Liabilities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Liabilities at Fair Value	(11,057)	(9,999)
Cash Instruments Liabilities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Liabilities at Fair Value	(194)	(273)
Cash Instruments Liabilities [Member] | U.S. Government and Agency Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Liabilities at Fair Value	(10,970)	(9,961)
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]
Trading Cash Instruments Liabilities at Fair Value	(10,959)	(9,914)
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]
Trading Cash Instruments Liabilities at Fair Value	(11)	(47)
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]
Trading Cash Instruments Liabilities at Fair Value	(25,511)	(23,424)
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]
Trading Cash Instruments Liabilities at Fair Value	(23,065)	(21,213)
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]
Trading Cash Instruments Liabilities at Fair Value	(2,445)	(2,205)
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]
Trading Cash Instruments Liabilities at Fair Value	(1)	(6)
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]
Trading Cash Instruments Liabilities at Fair Value	(27)	(32)
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]
Trading Cash Instruments Liabilities at Fair Value	(26)	(31)
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]
Trading Cash Instruments Liabilities at Fair Value	(1)	(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]
Trading Cash Instruments Liabilities at Fair Value	(2)	(2)
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]
Trading Cash Instruments Liabilities at Fair Value	(2)	(2)
Cash Instruments Liabilities [Member] | Corporate debt instruments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Liabilities at Fair Value	(8,344)	(7,862)
Cash Instruments Liabilities [Member] | Corporate debt instruments [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Liabilities at Fair Value	(7)	(115)
Cash Instruments Liabilities [Member] | Corporate debt instruments [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Liabilities at Fair Value	(8,160)	(7,494)
Cash Instruments Liabilities [Member] | Corporate debt instruments [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Liabilities at Fair Value	(177)	(253)
Cash Instruments Liabilities [Member] | State and Municipal Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Liabilities at Fair Value		(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]
Trading Cash Instruments Liabilities at Fair Value		(2)
Cash Instruments Liabilities [Member] | Other debt obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Liabilities at Fair Value	(5)
Cash Instruments Liabilities [Member] | Other debt obligations [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Liabilities at Fair Value	(5)
Cash Instruments Liabilities [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Liabilities at Fair Value	(29,431)	(23,744)
Cash Instruments Liabilities [Member] | Equity Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Liabilities at Fair Value	(29,037)	(23,519)
Cash Instruments Liabilities [Member] | Equity Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Liabilities at Fair Value	(379)	(212)
Cash Instruments Liabilities [Member] | Equity Securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Liabilities at Fair Value	(15)	(13)
Cash Instruments Liabilities [Member] | Commodities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Liabilities at Fair Value	(29)	(6)
Cash Instruments Liabilities [Member] | Commodities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading Cash Instruments Liabilities at Fair Value	$ (29)	$ (6)