Derivatives and Hedging Activities - Fair Value of Derivatives, 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
Derivative [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Beginning Balance	$ 2,430	$ 338	$ 495	$ 706
Net Realized Gains / (Losses)	17	(22)	(110)	158
Net Unrealized Gains / (Losses)	(171)	891	620	967
Purchases	43	79	191	197
Sales	(38)	(510)	(279)	(972)
Settlements	(194)	1,665	622	286
Transfers Into Level 3	119	(202)	500	(165)
Transfers Out Of Level 3	86	154	253	1,216
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Ending Balance	2,292	2,393	2,292	2,393
Interest Rate Contract [Member]
Derivative [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Beginning Balance	56	(78)	(398)	(40)
Net Realized Gains / (Losses)	(23)	(27)	(43)	(10)
Net Unrealized Gains / (Losses)	(48)	1	129	(4)
Purchases		2	3	5
Sales	(2)	(1)	(5)	(32)
Settlements	61	10	95	31
Transfers Into Level 3	9	(112)	304	(105)
Transfers Out Of Level 3	1	5	(31)	(45)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Ending Balance	54	(200)	54	(200)
Credit Risk Contract [Member]
Derivative [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Beginning Balance	2,942	2,968	2,793	3,530
Net Realized Gains / (Losses)	7	39	(50)	147
Net Unrealized Gains / (Losses)	(31)	416	359	553
Purchases	12	32	68	56
Sales	(6)	(46)	(38)	(151)
Settlements	(110)	109	(393)	(700)
Transfers Into Level 3	101	(5)	191	127
Transfers Out Of Level 3	(4)	(219)	(19)	(268)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Ending Balance	2,911	3,294	2,911	3,294
Foreign Exchange Contract [Member]
Derivative [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Beginning Balance	17	(149)	(34)	(267)
Net Realized Gains / (Losses)	(12)	(18)	(39)	(71)
Net Unrealized Gains / (Losses)	(14)	183	2	301
Purchases	1	4	15	31
Sales			(4)	(8)
Settlements	39	37	84	108
Transfers Into Level 3		(4)	1	(19)
Transfers Out Of Level 3	1	107	7	85
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Ending Balance	32	160	32	160
Commodity Contract [Member]
Derivative [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Beginning Balance	(222)	(54)	(262)	(1,142)
Net Realized Gains / (Losses)	(2)	1	22	9
Net Unrealized Gains / (Losses)	(25)	(27)	34	(68)
Purchases	1	2	27
Sales	(4)	(56)	(118)	(87)
Settlements	34	(4)	12	(95)
Transfers Into Level 3	6	7	10	(20)
Transfers Out Of Level 3	210	154	273	1,426
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Ending Balance	(2)	23	(2)	23
Equity Contract [Member]
Derivative [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Beginning Balance	(363)	(2,349)	(1,604)	(1,375)
Net Realized Gains / (Losses)	47	(17)		83
Net Unrealized Gains / (Losses)	(53)	318	96	185
Purchases	29	39	78	105
Sales	(26)	(407)	(114)	(694)
Settlements	(218)	1,513	824	942
Transfers Into Level 3	3	(88)	(6)	(148)
Transfers Out Of Level 3	(122)	107	23	18
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Ending Balance	$ (703)	$ (884)	$ (703)	$ (884)