Price Risk Management Activities, Hedging Instruments by Consolidated Balance Sheet Location (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	$ 901	$ 915
Derivative liability, fair value, gross liability	999	900
Commodity Future [Member] | Trade Accounts Receivable [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	861	874
Derivative asset, fair value, gross liability	974	872
Commodity Swap [Member] | Trade Accounts Receivable [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	27	32
Derivative asset, fair value, gross liability	13	21
Commodity Option [Member] | Trade Accounts Receivable [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	7	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	8	5
Foreign Currency Contracts [Member] | Trade Accounts Receivable [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	6	3
Derivative asset, fair value, gross liability	0	$ 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	$ 1