Derivatives and Hedging Activities - Fair Value, Derivatives, Measurement Inputs, Disclosure (Detail) $ in Millions	Mar. 31, 2020 USD ($) MMBTU $ / bbl	Dec. 31, 2019 USD ($) MMBTU $ / bbl	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Fair Value Measurement Inputs Disclosure [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Derivative Contracts Net Value, Ending Balance | $	$ 1,660	$ 25	$ (688)	$ 590
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 | $	$ 266	$ 89	(19)	(109)
Interest Rate Contract [Member] | Level 3 [Member] | Measurement Input, Correlation [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.52	0.52
Interest Rate Contract [Member] | Level 3 [Member] | Measurement Input, Median Correlation [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.62	0.60
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	0.70
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	0.61
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 | $	$ 2,518	$ 1,877	1,874	1,672
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	1.54	0.96
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	0.95	0.53
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	0.32	0.38
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	0.25	0.32
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	0.35	0.31
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	0.38	0.25
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 | $	$ 61	$ (211)	29	461
Foreign Exchange Contract [Member] | Level 3 [Member] | Measurement Input, Average Correlation [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.39	0.37
Foreign Exchange Contract [Member] | Level 3 [Member] | Measurement Input, Median Correlation [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.41	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 | $	$ 388	$ 247	145	112
Commodity Contract [Member] | Level 3 [Member] | Measurement Input, Average Volatility [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.45	0.26
Commodity Contract [Member] | Level 3 [Member] | Measurement Input, Median Volatility [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.42	0.25
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	0.15	0.16
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	0.09	0.17
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	3.92	9.82
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	1.26	11.15
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 | $	$ (1,573)	$ (1,977)	$ (2,717)	$ (1,546)
Equity Contract [Member] | Level 3 [Member] | Measurement Input, Average Correlation [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	(0.53)	(0.42)
Equity Contract [Member] | Level 3 [Member] | Measurement Input, Median Correlation [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.62	0.45
Equity Contract [Member] | Level 3 [Member] | Measurement Input, Average Volatility [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.27	0.14
Equity Contract [Member] | Level 3 [Member] | Measurement Input, Median Volatility [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.20	0.07
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)	(0.42)
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	0.02	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	0.01	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	0.01	0.10
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	0.20
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	0.15	0.09
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	1.31	1.93
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	4.71	4.86
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)	(0.70)
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	0.02
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	0.81
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	8.72	5.59
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	0.95	0.90
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	0.70	0.60
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	1.87	0.57
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	1.50	1.69
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	18.31	19.77
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	0.99
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	1.29	0.72