Price Risk Management Activities, Hedging Instruments by Consolidated Balance Sheet Location (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	$ 719	$ 685
Derivative liability, fair value, gross liability	748	563
Future [Member] | Commodity Contracts [Member] | Trade Accounts Receivable [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	700	648
Derivative asset, fair value, gross liability	720	522
Swap [Member] | Commodity Contracts [Member] | Trade Accounts Receivable [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	11	30
Derivative asset, fair value, gross liability	17	33
Options Held [Member] | Commodity Contracts [Member] | Trade Accounts Receivable [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	8	4
Derivative asset, fair value, gross liability	3	2
Forward Contracts [Member] | 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	5	6
Forward Contracts [Member] | 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
Forward Contracts [Member] | 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	$ 3