Fair Value Option - Level 3 Rollforward (Detail) - Other Financial Liabilities [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 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	$ (21,036)	$ (19,397)
Net realized gains / (losses)	(130)	(79)
Net unrealized gains/(losses)	3,160	(1,494)
Issuances	(7,643)	(3,036)
Settlements	5,157	3,307
Transfers into level 3	(1,596)	(571)
Transfers out of level 3	438	351
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	(21,650)	(20,919)
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	(4,023)	(3,168)
Net realized gains / (losses)	(11)	(1)
Net unrealized gains/(losses)	117	(142)
Issuances	(335)	(197)
Settlements	309	111
Transfers into level 3	(121)	(16)
Transfers out of level 3	68	62
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	(3,996)	(3,351)
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	(30)	(29)
Net unrealized gains/(losses)	3	(4)
Settlements	15	4
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	(12)	(29)
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	(386)	(170)
Net realized gains / (losses)	(44)	11
Net unrealized gains/(losses)	107	(10)
Issuances	(14)	(11)
Settlements	92	8
Transfers into level 3	(985)	(20)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	(1,230)	(192)
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	(5,707)	(4,076)
Net realized gains / (losses)	(11)	7
Net unrealized gains/(losses)	1,538	(425)
Issuances	(3,954)	(2,155)
Settlements	2,718	1,344
Transfers into level 3	(270)	(338)
Transfers out of level 3	275	130
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	(5,411)	(5,513)
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	(10,741)	(11,823)
Net realized gains / (losses)	(72)	(103)
Net unrealized gains/(losses)	1,571	(912)
Issuances	(3,332)	(666)
Settlements	2,023	1,840
Transfers into level 3	(220)	(197)
Transfers out of level 3	95	159
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	(10,676)	(11,702)
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	(149)	(131)
Net realized gains / (losses)	8	7
Net unrealized gains/(losses)	(176)	(1)
Issuances	(8)	(7)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	$ (325)	$ (132)