Contingencies and Commitments - Aggregate Undiscounted Commitments on Gathering Processing and Transportation Agreements Table (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Disclosure Aggregate Undiscounted Commitments On Gathering Processing And Transportation Agreements [Abstract]
Service Agreement Commitment 2012	$ 1,540
Service Agreement Commitment 2013	1,988
Service Agreement Commitment 2014	1,801
Service Agrement Commitment 2015	1,895
Service Agreement Commitment 2016	1,922
Service Agreement Commitment 2017 - 2099	9,344
Service Commitment Agreement Total	$ 18,490