Stock-Based Compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended						1 Months Ended	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Jun. 30, 2014 Equity [Member]	Jun. 30, 2013 Equity [Member]	Jun. 30, 2014 Equity [Member]	Jun. 30, 2013 Equity [Member]	Jun. 30, 2014 Stockholder Value Appreciation Program [Member]	Jun. 30, 2013 Stockholder Value Appreciation Program [Member]	Jun. 30, 2014 Stockholder Value Appreciation Program [Member]	Jun. 30, 2013 Stockholder Value Appreciation Program [Member]	Jun. 30, 2014 Stockholder Value Appreciation Program [Member] $27.50 [Member]	Jun. 30, 2014 Stockholder Value Appreciation Program [Member] $32.50 [Member]	Jun. 30, 2014 Stockholder Value Appreciation Program [Member] $37.50 [Member]	Jun. 30, 2014 Stockholder Value Appreciation Program [Member] $42.50 [Member]	Aug. 31, 2014 Stockholder Value Appreciation Program [Member] Subsequent Event [Member]	Jun. 30, 2014 Cash-Settled Restricted Stock Units [Member]	Jun. 30, 2013 Cash-Settled Restricted Stock Units [Member]	Jun. 30, 2014 Cash-Settled Restricted Stock Units [Member]	Jun. 30, 2013 Cash-Settled Restricted Stock Units [Member]	Jun. 30, 2014 Liability [Member]	Jun. 30, 2013 Liability [Member]	Jun. 30, 2014 Liability [Member]	Jun. 30, 2013 Liability [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 61	$ 12	$ 92	$ 24		$ 11	$ 11	$ 22	$ 23	$ 40	$ 0	$ 54	$ 0						$ 10	$ 1	$ 16	$ 1	$ 50	$ 1	$ 70	$ 1
Capitalized in oil and gas properties	26	4	40	7
Net stock-based compensation expense	35	8	52	17
Vesting Period																					3 years 0 months 0 days
Number of restricted stock shares vested			332,000																		283,000	38,000
Number of restricted stock shares outstanding	3,751,000		3,751,000		3,705,000														1,000,000		1,000,000
Fair value of units vested during the period																					7	1
Nonvested Awards, Total Compensation Cost Not yet Recognized	104		104							13		13							19		19
Weighted Average Volatility Rate												33.00%
Liability Value	70		70							46		46
SVAP Price Threshold														$ 27.50	$ 32.50	$ 37.50	$ 42.50
SVAP Expected Term												1 year 6 months
Fair Value Assumptions, Risk Free Interest Rate												0.25%
Cash payment to settle liability awards																		$ 13
Stock-Based Compensation (Textuals) [Abstract]
Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition			4 years
Last reported sales price of our common stock on the New York Stock Exchange per share	$ 44.20		$ 44.20