Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue from Contract with Customer, Including Assessed Tax									$ 3,222,093
Regulated Operating Revenue, Other									39,829	$ 41,854	$ 35,299
Revenues									3,346,496	3,460,276	3,164,301
Natural Gas, US Regulated [Member]
Revenue from Contract with Customer, Including Assessed Tax									849,898
Other Revenue From Contracts with Customers [Member]
Revenue from Contract with Customer, Including Assessed Tax									234,187
Decoupling over-collection [Domain]
Regulated Operating Revenue, Other									(22,852)
Other Non-606 Revenue [Member]
Regulated Operating Revenue, Other									147,255
Electricity, US Regulated [Member]
Revenue from Contract with Customer, Including Assessed Tax									2,138,008
Subsidiaries [Member]
Regulated Operating Revenue, Other									39,829	41,854	35,616
Revenues	$ 985,172	$ 651,464	$ 671,852	$ 1,038,008	$ 1,002,900	$ 660,377	$ 719,767	$ 1,077,232	$ 3,346,496	$ 3,460,276	$ 3,164,618