Price Risk Management Activities, Hedging Instruments by Consolidated Balance Sheet Location (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	$ 1,438	$ 894
Derivative liability, fair value, gross liability	1,480	982
Commodity Future [Member] | Receivable, Net [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	1,398	875
Derivative asset, fair value, gross liability	1,426	955
Commodity Swap [Member] | Receivable, Net [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	11	11
Derivative asset, fair value, gross liability	11	11
Commodity Swap [Member] | Accounts Payable [Member]
Fair Values of Derivative Instruments
Derivative liability, fair value, gross asset	0
Derivative liability, fair value, gross liability	1
Commodity Option [Member] | Receivable, Net [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	27	8
Derivative asset, fair value, gross liability	29	3
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	13	6
Foreign Currency Contracts [Member] | Receivable, Net [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	2
Derivative asset, fair value, gross liability	$ 0
Foreign Currency Contracts [Member] | Accrued Expenses [Member]
Fair Values of Derivative Instruments
Derivative liability, fair value, gross asset		0
Derivative liability, fair value, gross liability		$ 7