Fair Value Option - Level 3 Rollforward (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Other Financial Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Beginning Balance	$ 48	$ 42	$ 45	$ 56
Net Realized Gains / (Losses)	1		2	1
Net Unrealized Gains / (Losses)	1		1	(4)
Purchases	6	2	10	6
Sales		(3)		(3)
Issuances	0	0	0	0
Settlements	(1)	1	(3)	(21)
Transfers Into Level 3				7
Transfers Out Of Level 3	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance	55	42	55	42
Other Financial Assets [Member] | Receivables from Customers and Counterparties 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, Asset Value, Beginning Balance	48	42	45	56
Net Realized Gains / (Losses)	1		2	1
Net Unrealized Gains / (Losses)	1		1	(4)
Purchases	6	2	10	6
Sales		(3)		(3)
Issuances	0	0	0	0
Settlements	(1)	1	(3)	(21)
Transfers Into Level 3				7
Transfers Out Of Level 3	0	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value, Ending Balance	55	42	55	42
Other Financial Liabilities [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	(15,089)	(12,338)	(11,244)	(9,292)
Net Realized Gains / (Losses)	(23)	58	(76)	36
Net Unrealized Gains / (Losses)	(306)	770	(335)	787
Purchases	(3)	(10)	(10)	(10)
Sales			6	32
Issuances	(2,150)	(2,030)	(8,996)	(6,727)
Settlements	1,787	759	5,192	3,009
Transfers Into Level 3	(230)	(716)	(803)	(1,594)
Transfers Out Of Level 3	886	1,250	1,138	1,502
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	(15,128)	(12,257)	(15,128)	(12,257)
Other Financial Liabilities [Member] | 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	(2,936)	(1,680)	(2,215)	(1,065)
Net Realized Gains / (Losses)	(7)	(3)	(20)	(6)
Net Unrealized Gains / (Losses)		11	(208)	64
Issuances	(284)	(295)	(797)	(997)
Settlements	9	8	22	45
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	(3,218)	(1,959)	(3,218)	(1,959)
Other Financial Liabilities [Member] | Securities Sold under Agreements to Repurchase 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	(76)	(82)	(71)	(124)
Net Unrealized Gains / (Losses)			(6)	(1)
Settlements	1	16	2	59
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	(75)	(66)	(75)	(66)
Other Financial Liabilities [Member] | 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	(688)	(1,479)	(549)	(1,091)
Net Realized Gains / (Losses)	(1)	(4)	(4)	(20)
Net Unrealized Gains / (Losses)	(9)	64	(33)	84
Purchases	(3)	(10)	(8)	(10)
Sales			6	32
Issuances	(1)	(125)	(141)	(630)
Settlements	191	84	228	290
Transfers Into Level 3	(106)	(312)	(116)	(481)
Transfers Out Of Level 3	1	1	1	45
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	(616)	(1,781)	(616)	(1,781)
Other Financial Liabilities [Member] | 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	(4,654)	(4,490)	(4,133)	(3,712)
Net Realized Gains / (Losses)		66	(33)	62
Net Unrealized Gains / (Losses)	(218)	548	(98)	356
Issuances	(692)	(1,023)	(3,327)	(2,735)
Settlements	1,208	552	3,522	1,882
Transfers Into Level 3	(76)	(154)	(427)	(669)
Transfers Out Of Level 3	760	62	824	377
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	(3,672)	(4,439)	(3,672)	(4,439)
Other Financial Liabilities [Member] | 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	(6,626)	(3,462)	(4,224)	(2,585)
Net Realized Gains / (Losses)	(19)	(2)	(27)	(4)
Net Unrealized Gains / (Losses)	(88)	155	21	292
Purchases			(2)
Issuances	(1,160)	(586)	(4,676)	(2,364)
Settlements	378	98	1,417	726
Transfers Into Level 3	(48)	(227)	(260)	(421)
Transfers Out Of Level 3	125	62	313	394
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	(7,438)	(3,962)	(7,438)	(3,962)
Other Financial Liabilities [Member] | Other Liabilities and Accrued Expenses 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	(109)	(1,145)	(52)	(715)
Net Realized Gains / (Losses)	4	1	8	4
Net Unrealized Gains / (Losses)	9	(8)	(11)	(8)
Issuances	(13)	(1)	(55)	(1)
Settlements		1	1	7
Transfers Into Level 3		(23)		(23)
Transfers Out Of Level 3		1,125		686
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value, Ending Balance	$ (109)	$ (50)	$ (109)	$ (50)