General (Details)	6 Months Ended
Jun. 30, 2012 OwnedAndOperatedCompanies OperatingSegments
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operating segments	8
Electric utility companies in the Western United States	1
Electric and natural gas utility companies in the Midwestern United States	1
Interstate natural gas pipeline companies in the United States	2
Electricity distribution companies in Great Britain	2

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

No definition available.

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