Fair Value Option - Level 3 Rollforward (Detail) - Other Financial Liabilities [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Beginning Balance	$ (25,963)	$ (20,819)	$ (21,036)	$ (19,397)
Net realized gains / (losses)	(112)	(135)	(244)	(307)
Net unrealized gains/(losses)	(354)	(185)	347	(1,839)
Issuances	(6,974)	(3,964)	(18,633)	(8,693)
Settlements	6,911	3,910	14,348	9,509
Transfers into level 3	(1,756)	(570)	(2,857)	(1,112)
Transfers out of level 3	344	670	171	746
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	(27,904)	(21,093)	(27,904)	(21,093)
Deposits at Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Beginning Balance	(4,217)	(3,622)	(4,023)	(3,168)
Net realized gains / (losses)	(4)			(3)
Net unrealized gains/(losses)	(68)	(129)	(142)	(398)
Issuances	(124)	(267)	(4,054)	(661)
Settlements	235	150	4,083	272
Transfers into level 3	(38)	(136)	(69)	(59)
Transfers out of level 3	66	58	55	71
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	(4,150)	(3,946)	(4,150)	(3,946)
Repurchase Agreements at Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Beginning Balance	(10)	(28)	(30)	(29)
Net unrealized gains/(losses)		1	(2)	(2)
Settlements	8	2	30	6
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	(2)	(25)	(2)	(25)
Other Secured Financings at Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Beginning Balance	(1,773)	(202)	(386)	(170)
Net realized gains / (losses)	7	4	13	19
Net unrealized gains/(losses)	(67)	(5)	(12)	(24)
Issuances	(10)	(1)	(847)	(20)
Settlements	79	3	332	14
Transfers into level 3	(1,299)	(133)	(2,163)	(153)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	(3,063)	(334)	(3,063)	(334)
Unsecured Short-Term Borrowings Including Current Portion of Unsecured Long-Term Borrowings at Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Beginning Balance	(6,806)	(5,026)	(5,707)	(4,076)
Net realized gains / (losses)	(58)	(50)	(109)	(99)
Net unrealized gains/(losses)	(42)	34	458	(238)
Issuances	(4,879)	(2,147)	(7,605)	(4,085)
Settlements	4,295	1,982	5,571	3,270
Transfers into level 3	(280)	(159)	(234)	(217)
Transfers out of level 3	196	383	52	462
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	(7,574)	(4,983)	(7,574)	(4,983)
Unsecured Long-Term Borrowings at Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Beginning Balance	(12,837)	(11,769)	(10,741)	(11,823)
Net realized gains / (losses)	(64)	(96)	(171)	(244)
Net unrealized gains/(losses)	(167)	(60)	225	(1,110)
Issuances	(1,949)	(1,542)	(6,099)	(3,907)
Settlements	2,294	1,773	4,332	5,947
Transfers into level 3	(139)	(142)	(390)	(683)
Transfers out of level 3	82	229	64	213
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	(12,780)	(11,607)	(12,780)	(11,607)
Other Liabilities at Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Beginning Balance	(320)	(172)	(149)	(131)
Net realized gains / (losses)	7	7	23	20
Net unrealized gains/(losses)	(10)	(26)	(180)	(67)
Issuances	(12)	(7)	(28)	(20)
Transfers into level 3			(1)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	$ (335)	$ (198)	$ (335)	$ (198)