Inventory, Linefill and Base Gas and Long-term Inventory (Details) bbl in Thousands, Mcf in Thousands, $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($) $ / bbl $ / Mcf Mcf bbl	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) $ / bbl $ / Mcf Mcf bbl
Inventory by category
Inventory	$ 837		$ 891
Linefill and base gas	910		930
Long-term inventory	166		186
Total	1,913		2,007
Inventory-related disclosures
Charge related to the write-down of inventory	25	$ 37
Crude oil
Inventory by category
Inventory	475		304
Linefill and base gas	724		744
Long-term inventory	$ 143		$ 136
Inventory, Volumes (in barrels or in Mcf) | bbl	11,796		6,465
Linefill and base gas, Volumes (in barrels or in Mcf) | bbl	12,327		11,810
Long-term inventory, Volumes (in barrels or in Mcf) | bbl	3,434		2,582
Inventory, Price/Unit of measure (in dollars per unit) | $ / bbl	40.27		47.02
Linefill and base gas, Price/Unit of measure (in dollars per unit) | $ / bbl	58.73		63.00
Long-term inventory, Price/Unit of measure (in dollars per unit) | $ / bbl	41.64		52.67
NGL
Inventory by category
Inventory	$ 272		$ 454
Linefill and base gas	45		52
Long-term inventory	$ 23		$ 50
Inventory, Volumes (in barrels or in Mcf) | bbl	18,461		13,553
Linefill and base gas, Volumes (in barrels or in Mcf) | bbl	1,348		1,212
Long-term inventory, Volumes (in barrels or in Mcf) | bbl	1,652		1,681
Inventory, Price/Unit of measure (in dollars per unit) | $ / bbl	14.73		33.50
Linefill and base gas, Price/Unit of measure (in dollars per unit) | $ / bbl	33.38		42.90
Long-term inventory, Price/Unit of measure (in dollars per unit) | $ / bbl	13.92		29.74
Natural gas
Inventory by category
Inventory	$ 48		$ 102
Linefill and base gas	$ 141		$ 134
Inventory, Volumes (in barrels or in Mcf) | Mcf	17,923		32,317
Linefill and base gas, Volumes (in barrels or in Mcf) | Mcf	30,812		28,612
Inventory, Price/Unit of measure (in dollars per unit) | $ / Mcf	2.68		3.16
Linefill and base gas, Price/Unit of measure (in dollars per unit) | $ / Mcf	4.58		4.68
Other
Inventory by category
Inventory	$ 42		$ 31