Stock-Based Compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 75	$ 47	$ 40
Capitalized in oil and gas properties	(20)	(12)	(11)
Net stock-based compensation expense	55	35	29
Number of restricted stock shares vested	1,195,000	1,066,000	925,000
Number of restricted stock shares outstanding	3,705,000	2,809,000	2,480,000	2,494,000
Fair value of units vested during the period	47	44	32
Share Based Compensation Arrangement Exercise Rate	20.00%
Nonvested Awards, Total Compensation Cost Not yet Recognized	116
SVAP Price Threshold	$ 27.50
SVAP Incremental Price Threshold	$ 5
Stock-Based Compensation (Textuals) [Abstract]
Unrecognized net operating loss related to Stock Based Compensation	102
Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	5 years
Last reported sales price of our common stock on the New York Stock Exchange per share	$ 24.63
Equity [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	48	46	37
Liability [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	27	1	3
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reduction factor multiplied by number of shares awarded	1
Additional shares available for issuance	2,700,000
Cash-Settled Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service Period	3 years
Number of restricted stock shares vested	85,000	44,000
Number of restricted stock shares outstanding	1,200,000
Nonvested Awards, Total Compensation Cost Not yet Recognized	15
Liability Settlements	2	2
Stockholder Value Appreciation Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service Period	2 years
Nonvested Awards, Total Compensation Cost Not yet Recognized	14
Weighted Average Volatility Rate	39.30%
Liability Value	5
Liability Settlements	13
Employee Service Shared-based Compensation, Nonvested Awards, Compensation Cost Not yet Paid	$ 19
Fair Value Assumptions, Risk Free Interest Rate	0.38%
Service - Based Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of restricted stock shares vested	1,195,000	977,000	836,000
Number of restricted stock shares outstanding	2,999,000	2,371,000	2,123,000	2,178,000
Performance Market Based Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of restricted stock shares vested	0	89,000	89,000
Number of restricted stock shares outstanding	706,000	438,000	357,000	316,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Reduction factor multiplied by number of shares awarded	1.87
Additional shares available for issuance	1,500,000