Derivatives and Hedging Activities - Fair Value, Derivatives, Measurement Inputs, Disclosure (Detail) $ in Millions	Dec. 31, 2019 USD ($) $ / bbl MMBTU	Dec. 31, 2018 USD ($) MMBTU $ / bbl	Dec. 31, 2017 USD ($)
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Ending Balance | $	$ 25	$ 590	$ (288)
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 | $	$ 89	$ (109)	(410)
Interest Rate Contract [Member] | Level 3 [Member] | Measurement Input, Average Correlation [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.52	0.66
Interest Rate Contract [Member] | Level 3 [Member] | Measurement Input, Median Correlation [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.60	0.64
Interest Rate Contract [Member] | Level 3 [Member] | Measurement Input, Average Volatility [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.70	0.74
Interest Rate Contract [Member] | Level 3 [Member] | Measurement Input, Median Volatility [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.61	0.65
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 | $	$ 1,877	$ 1,672	1,505
Credit Risk Contract [Member] | Level 3 [Member] | Measurement Input, Average Credit Spread [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.96	1.09
Credit Risk Contract [Member] | Level 3 [Member] | Measurement Input, Median Credit Spread [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.53	0.63
Credit Risk Contract [Member] | Level 3 [Member] | Measurement Input, , Average Upfront Credit Points [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.38	0.44
Credit Risk Contract [Member] | Level 3 [Member] | Measurement Input, , Median Upfront Credit Points [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.32	0.40
Credit Risk Contract [Member] | Level 3 [Member] | Measurement Input, Average Recovery Rate [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.31	0.40
Credit Risk Contract [Member] | Level 3 [Member] | Measurement Input, Median Recovery Rate [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.25	0.40
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 | $	$ (211)	$ 461	(181)
Foreign Exchange Contract [Member] | Level 3 [Member] | Measurement Input, Average Correlation [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.37	0.40
Foreign Exchange Contract [Member] | Level 3 [Member] | Measurement Input, Median Correlation [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.36	0.36
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 | $	$ 247	$ 112	47
Commodity Contract [Member] | Level 3 [Member] | Measurement Input, Average Volatility [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.26	0.28
Commodity Contract [Member] | Level 3 [Member] | Measurement Input, Median Volatility [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.25	0.27
Commodity Contract [Member] | Natural Gas [Member] | Level 3 [Member] | Measurement Input, Average Spread [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs | MMBTU	0.16	0.26
Commodity Contract [Member] | Natural Gas [Member] | Level 3 [Member] | Measurement Input, Median Spread [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs | MMBTU	0.17	0.30
Commodity Contract [Member] | Oil [Member] | Level 3 [Member] | Measurement Input, Average Spread [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs | $ / bbl	9.82	4.53
Commodity Contract [Member] | Oil [Member] | Level 3 [Member] | Measurement Input, Median Spread [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs | $ / bbl	11.15	3.94
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 | $	$ (1,977)	$ (1,546)	$ (1,249)
Equity Contract [Member] | Level 3 [Member] | Measurement Input, Average Volatility [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.14	0.20
Equity Contract [Member] | Level 3 [Member] | Measurement Input, Median Volatility [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.07	0.18
Minimum [Member] | Interest Rate Contract [Member] | Level 3 [Member] | Measurement Input, Correlation [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	(0.42)	(0.10)
Minimum [Member] | Interest Rate Contract [Member] | Level 3 [Member] | Measurement Input, Price Volatility [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.31	0.31
Minimum [Member] | Credit Risk Contract [Member] | Level 3 [Member] | Measurement Input, Credit Spread [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.01	0.01
Minimum [Member] | Credit Risk Contract [Member] | Level 3 [Member] | Measurement Input, Upfront Credit Points [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.02	0.02
Minimum [Member] | Credit Risk Contract [Member] | Level 3 [Member] | Measurement Input, Recovery Rate [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.10	0.25
Minimum [Member] | Foreign Exchange Contract [Member] | Level 3 [Member] | Measurement Input, Correlation [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.20	0.10
Minimum [Member] | Commodity Contract [Member] | Level 3 [Member] | Measurement Input, Price Volatility [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.09	0.10
Minimum [Member] | Commodity Contract [Member] | Natural Gas [Member] | Level 3 [Member] | Measurement Input, Spread [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs | MMBTU	1.93	2.32
Minimum [Member] | Commodity Contract [Member] | Oil [Member] | Level 3 [Member] | Measurement Input, Spread [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs | $ / bbl	4.86	3.44
Minimum [Member] | Equity Contract [Member] | Level 3 [Member] | Measurement Input, Correlation [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	(0.70)	(0.68)
Minimum [Member] | Equity Contract [Member] | Level 3 [Member] | Measurement Input, Average Correlation [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.42	0.48
Minimum [Member] | Equity Contract [Member] | Level 3 [Member] | Measurement Input, Price Volatility [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.02	0.03
Maximum [Member] | Interest Rate Contract [Member] | Level 3 [Member] | Measurement Input, Correlation [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.81	0.86
Maximum [Member] | Interest Rate Contract [Member] | Level 3 [Member] | Measurement Input, Price Volatility [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	1.50	1.50
Maximum [Member] | Credit Risk Contract [Member] | Level 3 [Member] | Measurement Input, Credit Spread [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	5.59	8.10
Maximum [Member] | Credit Risk Contract [Member] | Level 3 [Member] | Measurement Input, Upfront Credit Points [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.90	0.99
Maximum [Member] | Credit Risk Contract [Member] | Level 3 [Member] | Measurement Input, Recovery Rate [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.60	0.70
Maximum [Member] | Foreign Exchange Contract [Member] | Level 3 [Member] | Measurement Input, Correlation [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.70	0.70
Maximum [Member] | Commodity Contract [Member] | Level 3 [Member] | Measurement Input, Price Volatility [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.57	0.75
Maximum [Member] | Commodity Contract [Member] | Natural Gas [Member] | Level 3 [Member] | Measurement Input, Spread [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs | MMBTU	1.69	4.68
Maximum [Member] | Commodity Contract [Member] | Oil [Member] | Level 3 [Member] | Measurement Input, Spread [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs | $ / bbl	19.77	16.62
Maximum [Member] | Equity Contract [Member] | Level 3 [Member] | Measurement Input, Correlation [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.99	0.97
Maximum [Member] | Equity Contract [Member] | Level 3 [Member] | Measurement Input, Average Correlation [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.45	0.51
Maximum [Member] | Equity Contract [Member] | Level 3 [Member] | Measurement Input, Price Volatility [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.72	1.02