Contingencies and Commitments - Aggregate Undiscounted Commitments on Gathering Processing and Transportation Agreements Table (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Contractual Obligation, Fiscal Year Maturity [Abstract]
Service Agreement Commitment 2013	$ 510
Service Agreement Commitment 2014	2,010
Service Agreement Commitment 2015	1,821
Service Agreement Commitment 2016	1,910
Service Agreement Commitment 2017	1,942
Service Agreement Commitment 2018 - 2099	9,546
Service Commitment Agreement Total	$ 17,739