Contingencies and Commitments - Aggregate Undiscounted Commitments on Gathering Processing and Transportation Agreements (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013
Contractual Obligation, Fiscal Year Maturity [Abstract]
Service Agreement Commitment 2013	$ 902
Service Agreement Commitment 2014	2,001
Service Agreement Commitment 2015	1,820
Service Agrement Commitment 2016	1,914
Service Agreement Commitment 2017	1,947
Service Agreement Commitment 2018 - 2099	9,477
Service Commitment Agreement Total	$ 18,061