Commitments and Contingencies (SM Energy Lawsuit) (Details) (SM Energy Litigation [Member], USD $) In Millions, unless otherwise specified	9 Months Ended
Sep. 30, 2013	Jan. 17, 2012
SM Energy Litigation [Member]
Loss Contingencies [Line Items]
Lawsuit filing date	December 20, 2011
Counterclaim date	January 17, 2012
Counterclaim amount		$ 6

States the date the complaint was formally filed in a court of law, in arbitration or mediation.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 4

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 9

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349

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