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General (Details)
9 Months Ended
Sep. 30, 2016
OperatingSegments
OwnedAndOperatedCompanies
Organization, Consolidation and Presentation of Financial Statements [Abstract]  
Number of reportable segments | OperatingSegments 8
Number of owned and operated utility companies in the United States 4
Number of states owned and operated utility companies serve customers 11
Number of owned and operated interstate natural gas pipeline companies in the United States 2
Number of owned and operated electricity distribution companies in Great Britain 2
Number of owned and operated electricity transmission companies in Canada 1
Number of owned and operated renewable energy businesses 1
Number of owned and operated residential real estate brokerage firms in the United States 1
Number of owned and operated residential real estate brokerage franchise networks in the United States 1