Price Risk Management Activities, Hedging Instruments by Consolidated Balance Sheet Location (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	$ 641	$ 2,796
Derivative liability, fair value, gross liability	599	2,687
Commodity Contracts [Member] | Receivable, Net [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	638	2,792
Derivative asset, fair value, gross liability	573	2,681
Physical Purchase Contracts [Member] | Inventories [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	0	0
Derivative asset, fair value, gross liability	6	5
Foreign Currency Contracts [Member] | Receivable, Net [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	3	4
Derivative asset, fair value, gross liability	0	0
Foreign Currency Contracts [Member] | Accrued Expenses [Member]
Fair Values of Derivative Instruments
Derivative liability, fair value, gross asset	0	0
Derivative liability, fair value, gross liability	$ 20	$ 1