Outstanding Oil Contracts That Are Not Designated For Hedge Accounting (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Oil contracts [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Total	$ 510
Natural gas contracts [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Total	103
Fixed Price Swaps With Sold Puts [Member] | Oil contracts [Member] | Year2015 [Member]
Derivative [Line Items]
Volume in MBbls	15,019,000
Collars With Sold Puts [Member] | Oil contracts [Member] | Year2015 [Member]
Derivative [Line Items]
Volume in MBbls	730,000
Fixed-price swaps | Oil contracts [Member] | Year2015 [Member]
Derivative [Line Items]
Volume in MBbls	2,275,000
Derivative, Swap Type, Average Fixed Price	90.20
Derivative Asset, Fair Value, Total	78
Fixed-price swaps | Natural gas contracts [Member] | Year2015 [Member]
Derivative [Line Items]
Derivative, Swap Type, Average Fixed Price	4.28
Derivative Asset, Fair Value, Total	$ 62