Derivatives and Hedging Activities - Fair Value, Derivatives, Measurement Inputs, Disclosure (Detail) $ in Millions	Sep. 30, 2016 USD ($) $ / Bbls $ / MMBTU	Dec. 31, 2015 USD ($) $ / Bbls $ / MMBTU	Jun. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Ending Balance	$ 2,292	$ 495	$ 2,430	$ 2,393	$ 338	$ 706
Interest Rate Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Ending Balance	54	(398)	56	(200)	(78)	(40)
Credit Risk Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Ending Balance	2,911	2,793	2,942	3,294	2,968	3,530
Foreign Exchange Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Ending Balance	32	(34)	17	160	(149)	(267)
Commodity Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Ending Balance	(2)	(262)	(222)	23	(54)	(1,142)
Equity Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Ending Balance	$ (703)	$ (1,604)	$ (363)	$ (884)	$ (2,349)	$ (1,375)
Minimum [Member] | Interest Rate Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Correlation	(10.00%)	(25.00%)
Fair Value Unobservable Input, Volatility	0.31%	0.31%
Minimum [Member] | Credit Risk Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Correlation	29.00%	46.00%
Fair Value Unobservable Inputs, Credit spreads	0.01%	0.01%
Fair Value Unobservable Inputs, Upfront Credit Points	0.00%	0.00%
Fair Value Unobservable Inputs, Recovery rates	1.00%	2.00%
Minimum [Member] | Foreign Exchange Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Correlation	25.00%	25.00%
Minimum [Member] | Commodity Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Input, Volatility	10.00%	11.00%
Minimum [Member] | Commodity Contract [Member] | Natural Gas [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Spread | $ / MMBTU	(2.20)	(1.32)
Minimum [Member] | Commodity Contract [Member] | Oil [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Spread | $ / Bbls	(11.15)	(10.64)
Minimum [Member] | Equity Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Correlation	(49.00%)	(65.00%)
Fair Value Unobservable Input, Volatility	5.00%	5.00%
Maximum [Member] | Interest Rate Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Correlation	86.00%	92.00%
Fair Value Unobservable Input, Volatility	1.51%	1.52%
Maximum [Member] | Credit Risk Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Correlation	92.00%	99.00%
Fair Value Unobservable Inputs, Credit spreads	9.60%	10.19%
Fair Value Unobservable Inputs, Upfront Credit Points	1.00%	1.00%
Fair Value Unobservable Inputs, Recovery rates	97.00%	97.00%
Maximum [Member] | Foreign Exchange Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Correlation	70.00%	70.00%
Maximum [Member] | Commodity Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Input, Volatility	67.00%	77.00%
Maximum [Member] | Commodity Contract [Member] | Natural Gas [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Spread | $ / MMBTU	4.01	4.15
Maximum [Member] | Commodity Contract [Member] | Oil [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Spread | $ / Bbls	64.66	65.29
Maximum [Member] | Equity Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Correlation	87.00%	94.00%
Fair Value Unobservable Input, Volatility	107.00%	76.00%
Average [Member] | Interest Rate Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Correlation	56.00%	53.00%
Fair Value Unobservable Input, Volatility	0.84%	0.84%
Average [Member] | Credit Risk Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Correlation	60.00%	68.00%
Fair Value Unobservable Inputs, Credit spreads	1.13%	1.29%
Fair Value Unobservable Inputs, Upfront Credit Points	0.42%	0.41%
Fair Value Unobservable Inputs, Recovery rates	61.00%	58.00%
Average [Member] | Foreign Exchange Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Correlation	51.00%	50.00%
Average [Member] | Commodity Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Input, Volatility	34.00%	35.00%
Average [Member] | Commodity Contract [Member] | Natural Gas [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Spread | $ / MMBTU	(0.06)	(0.05)
Average [Member] | Commodity Contract [Member] | Oil [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Spread | $ / Bbls	10.95	3.34
Average [Member] | Equity Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Correlation	44.00%	42.00%
Fair Value Unobservable Input, Volatility	25.00%	24.00%
Median [Member] | Interest Rate Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Correlation	60.00%	55.00%
Fair Value Unobservable Input, Volatility	0.57%	0.57%
Median [Member] | Credit Risk Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Correlation	59.00%	66.00%
Fair Value Unobservable Inputs, Credit spreads	0.68%	0.86%
Fair Value Unobservable Inputs, Upfront Credit Points	0.37%	0.40%
Fair Value Unobservable Inputs, Recovery rates	70.00%	70.00%
Median [Member] | Foreign Exchange Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Correlation	55.00%	51.00%
Median [Member] | Commodity Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Input, Volatility	34.00%	34.00%
Median [Member] | Commodity Contract [Member] | Natural Gas [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Spread | $ / MMBTU	(0.02)	(0.01)
Median [Member] | Commodity Contract [Member] | Oil [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Spread | $ / Bbls	6.92	(3.31)
Median [Member] | Equity Contract [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value Unobservable Inputs, Correlation	45.00%	48.00%
Fair Value Unobservable Input, Volatility	24.00%	23.00%