Fair Value Option - Financial Assets and Financial Liabilities by Level (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Resale agreements	$ 138,299	$ 139,220
Securities borrowed	30,003	23,142
Customer and other receivables	1,677	3,189
Total financial assets at fair value	169,979	165,551
Deposits	(21,570)	(21,060)
Repurchase agreements	(109,438)	(78,723)
Securities loaned	(2,622)	(3,241)
Other secured financings	(16,084)	(20,904)
Unsecured borrowings Short-term	(22,641)	(16,963)
Unsecured borrowings Long-term	(47,047)	(46,584)
Other liabilities	(204)	(132)
Total financial liabilities at fair value	(219,606)	(187,607)
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Resale agreements	138,299	139,220
Securities borrowed	30,003	23,142
Customer and other receivables	1,677	3,183
Total financial assets at fair value	169,979	165,545
Deposits	(17,624)	(17,892)
Repurchase agreements	(109,413)	(78,694)
Securities loaned	(2,622)	(3,241)
Other secured financings	(15,750)	(20,734)
Unsecured borrowings Short-term	(17,658)	(12,887)
Unsecured borrowings Long-term	(35,440)	(34,761)
Other liabilities	(6)	(1)
Total financial liabilities at fair value	(198,513)	(168,210)
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Customer and other receivables		6
Total financial assets at fair value		6
Deposits	(3,946)	(3,168)
Repurchase agreements	(25)	(29)
Other secured financings	(334)	(170)
Unsecured borrowings Short-term	(4,983)	(4,076)
Unsecured borrowings Long-term	(11,607)	(11,823)
Other liabilities	(198)	(131)
Total financial liabilities at fair value	$ (21,093)	$ (19,397)