Derivatives and Hedging Activities - Fair Value of Derivatives, Level 3 Rollforward (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Derivative [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Beginning Balance	$ (1,217)	$ 495
Net Realized Gains / (Losses)	(15)	(79)
Net Unrealized Gains / (Losses)	769	461
Purchases	79	115
Sales	(458)	(1,825)
Settlements	871	106
Transfers Into Level 3	(10)	(16)
Transfers Out Of Level 3	78	798
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Ending Balance	97	55
Interest Rate Contract [Member]
Derivative [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Beginning Balance	(381)	(398)
Net Realized Gains / (Losses)	(22)	(11)
Net Unrealized Gains / (Losses)	103	28
Purchases	4	3
Sales	(9)	(10)
Settlements	46	17
Transfers Into Level 3	(10)
Transfers Out Of Level 3	(13)	(12)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Ending Balance	(282)	(383)
Credit Risk Contract [Member]
Derivative [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Beginning Balance	2,504	2,793
Net Realized Gains / (Losses)	43	(26)
Net Unrealized Gains / (Losses)	(174)	210
Purchases	16	33
Sales	(20)	(57)
Settlements	(135)	(75)
Transfers Into Level 3	13	8
Transfers Out Of Level 3	(8)	(65)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Ending Balance	2,239	2,821
Foreign Exchange Contract [Member]
Derivative [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Beginning Balance	3	(34)
Net Realized Gains / (Losses)	(22)	(21)
Net Unrealized Gains / (Losses)	(13)	(5)
Purchases	2	6
Sales		(1)
Settlements	51	61
Transfers Into Level 3	(2)
Transfers Out Of Level 3	5	3
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Ending Balance	24	9
Commodity Contract [Member]
Derivative [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Beginning Balance	73	(262)
Net Realized Gains / (Losses)		(5)
Net Unrealized Gains / (Losses)	20	41
Purchases	13	47
Sales	(13)	(18)
Settlements	(21)	(37)
Transfers Into Level 3	(9)	(26)
Transfers Out Of Level 3	15	(31)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Ending Balance	78	(291)
Equity Contract [Member]
Derivative [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Beginning Balance	(3,416)	(1,604)
Net Realized Gains / (Losses)	(14)	(16)
Net Unrealized Gains / (Losses)	833	187
Purchases	44	26
Sales	(416)	(1,739)
Settlements	930	140
Transfers Into Level 3	(2)	2
Transfers Out Of Level 3	79	903
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Ending Balance	$ (1,962)	$ (2,101)