Price Risk Management Activities, Hedging Instruments by Consolidated Balance Sheet Location (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	$ 894	$ 915
Derivative liability, fair value, gross liability	982	900
Commodity Future [Member] | Trade Accounts Receivable [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	875	874
Derivative asset, fair value, gross liability	955	872
Commodity Swap [Member] | Trade Accounts Receivable [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	11	32
Derivative asset, fair value, gross liability	11	21
Commodity Option [Member] | Trade Accounts Receivable [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	8	6
Derivative asset, fair value, gross liability	3	2
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] | Trade Accounts Receivable [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset		3
Derivative asset, fair value, gross liability		$ 0
Foreign Currency Contracts [Member] | Accrued Liabilities [Member]
Fair Values of Derivative Instruments
Derivative liability, fair value, gross asset	0
Derivative liability, fair value, gross liability	$ 7