Segment Information Major Customers (Details) - Revenue [Member]	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Threshold for Reporting Customer Concentration [Member]
Revenue, Major Customer [Line Items]
Concentration Risk, Percentage	10.00%	10.00%
Customer A [Member]
Revenue, Major Customer [Line Items]
Concentration Risk, Percentage	10.00%
Customer A [Member] | Electricity Operating Segment [Member]
Revenue, Major Customer [Line Items]
Concentration Risk, Percentage	22.00%	18.00%
Customer A [Member] | Gas Operating Segment [Member]
Revenue, Major Customer [Line Items]
Concentration Risk, Percentage	11.00%
Customer A [Member] | Networks Operating Segment [Member]
Revenue, Major Customer [Line Items]
Concentration Risk, Percentage	11.00%
Customer B [Member] | Electricity Operating Segment [Member]
Revenue, Major Customer [Line Items]
Concentration Risk, Percentage	16.00%