Derivatives and Hedging Activities - Fair Value, Derivatives, Measurement Inputs, Disclosure (Detail) $ in Millions	Sep. 30, 2020 USD ($) MMBTU $ / bbl	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($) MMBTU $ / bbl	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	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 | $	$ 2,154	$ 3,060	$ 25	$ 663	$ 598	$ 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 | $	$ 255	311	$ 89	50	30	(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	0.60		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	(0.65)		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	0.53		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 | $	$ 1,986	2,327	$ 1,877	1,900	1,676	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	1.24		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	0.90		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	0.47		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	0.50		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	0.48		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	0.40		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 | $	$ (255)	(94)	$ (211)	(186)	(31)	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
Foreign Exchange Contract [Member] | Level 3 [Member] | Measurement Input, Average Volatility [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.20
Foreign Exchange Contract [Member] | Level 3 [Member] | Measurement Input, Median Volatility [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.20
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 | $	$ 195	331	$ 247	161	134	112
Commodity Contract [Member] | Level 3 [Member] | Measurement Input, Average Volatility [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.39		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	0.33		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	0.12		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	8.15		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	8.33		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 | $	$ (27)	$ 185	$ (1,977)	$ (1,262)	$ (1,211)	$ (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	0.50		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	0.55		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	0.24		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	0.22		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	(0.38)		(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	0.07		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	0.25		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] | Foreign Exchange Contract [Member] | Level 3 [Member] | Measurement Input, Price Volatility [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.19
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	0.14		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	1.44		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	4.73		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	0.03		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	7.48		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	0.90		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	0.90		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] | Foreign Exchange Contract [Member] | Level 3 [Member] | Measurement Input, Price Volatility [Member]
Fair Value Measurement Inputs Disclosure [Line Items]
Assets (Liabilities) significant unobservable Inputs	0.20
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	1.05		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	1.89		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	9.98		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	1.28		0.72