Acquisitions and Divestitures Aquisitions - Subsequent Events (Details) (Copano Energy, LLC [Member], USD $) In Millions, unless otherwise specified	Jan. 29, 2013 mi MMcf
Copano Energy, LLC [Member]
Business Acquisition [Line Items]
Business Acquisition, Cost of Acquired Entity, Purchase Price	$ 5,000
Business acquisition, percent of consideration comprised of units	100.00%
Business acquisition, unit exchange ratio	0.4563
Miles of pipe	6,900
Gas treating capacity in MMcf	315,000,000

The total cost of the acquired entity including the cash paid to shareholders of acquired entities, fair value of debt and equity securities issued to shareholders of acquired entities, the fair value of the liabilities assumed, and direct costs of the acquisition.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141

-Paragraph 51

-Subparagraph d

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_BusinessAcquisitionCostOfAcquiredEntityPurchasePrice
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant