Fair Value Measurements and Disclosures of Assets and Liabilities Measured on a Nonrecurring Basis (Details 2) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Asset Impairment Charges [Abstract]
Impaired Oil and Gas Properties	$ 500		$ 86		$ 104
Impaired Oil and Gas Properties, Net Book Value	600	[1]	199	[1]	332	[1]
Discount Rate for Impairment Model	10.00%
Quoted Prices in Active Markets (Level 1)
Asset Impairment Charges [Abstract]
Impaired Oil and Gas Properties	0	[2]	0	[2]	0	[2]
Significant Other Observable Inputs (Level 2)
Asset Impairment Charges [Abstract]
Impaired Oil and Gas Properties	0	[2]	0	[2]	0	[2]
Significant Unobservable Inputs (Level 3)
Asset Impairment Charges [Abstract]
Impaired Oil and Gas Properties	$ 100	[2]	$ 113	[2]	$ 228	[2]

[1] Amount represents net book value at the date of assessment.

[2] See Note 1. Summary of Significant Accounting Policies - Fair Value Measurements for a description of the fair value hierarchy.