Price Risk Management Activities, Effect of Derivative Instruments on Income and Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Commodity Contracts [Member]
Effect of Derivative Instruments on Income
Gain (loss) recognized in other comprehensive income (loss) on derivatives	$ (18)	$ (5)	$ (31)	$ 50
Commodity Contracts [Member] | Revenues [Member]
Effect of Derivative Instruments on Income
Gain (loss) reclassified from accumulated other comprehensive loss into income	(11)	19	(34)	45
Commodity Contracts [Member] | Revenues [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Effect of Derivative Instruments on Income
Gain (loss) recognized in income on derivatives	13	9	20	1
Commodity Contracts [Member] | Cost of Materials and Other [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Effect of Derivative Instruments on Income
Gain (loss) recognized in income on derivatives	21	140	(57)	(12)
Commodity Contracts [Member] | Operating Expenses (Excluding Depreciation and Amortization Expense) [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Effect of Derivative Instruments on Income
Gain (loss) recognized in income on derivatives	2	4	3	2
Foreign Currency Contracts [Member] | Cost of Materials and Other [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Effect of Derivative Instruments on Income
Gain (loss) recognized in income on derivatives	6	0	(2)	49
Foreign Currency Contracts [Member] | Other Income, Net [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Effect of Derivative Instruments on Income
Gain (loss) recognized in income on derivatives	$ 53	$ 60	$ 83	$ (105)