Price Risk Management Activities, Hedging Instruments by Consolidated Balance Sheet Location (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	$ 685	$ 3,133
Derivative liability, fair value, gross liability	563	2,925
Future [Member] | Commodity Contract [Member] | Trade Accounts Receivable [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	648	3,096
Derivative asset, fair value, gross liability	522	2,886
Swap [Member] | Commodity Contract [Member] | Trade Accounts Receivable [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	30	34
Derivative asset, fair value, gross liability	33	31
Options Held [Member] | Commodity Contract [Member] | Trade Accounts Receivable [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	4	2
Derivative asset, fair value, gross liability	2	3
Forward Contracts [Member] | Physical Purchase Contracts [Member] | Inventories [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	0	1
Derivative asset, fair value, gross liability	6	$ 5
Forward Contracts [Member] | Foreign Currency Contract [Member] | Trade Accounts Receivable [Member]
Fair Values of Derivative Instruments
Derivative asset, fair value, gross asset	3
Derivative asset, fair value, gross liability	$ 0