Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Regulated Operating Revenue, Other	$ 10,069	$ 11,318	$ 28,253	$ 29,356
Total operating revenue	651,464	660,377	2,361,324	2,457,376
Electricity, US Regulated [Member]
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	464,210		1,563,394
Natural Gas, US Regulated [Member]
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	101,995		594,572
Other Revenue From Contracts with Customers [Member]
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	67,217		148,581
Revenue from Contract with Customer [Member]
Disaggregation of Revenue [Line Items]
Total revenue from contracts with customers	633,422		2,306,547
Decoupling over-collection [Domain]
Disaggregation of Revenue [Line Items]
Regulated Operating Revenue, Other	(782)		(24,678)
Other Non-606 Revenue [Member]
Disaggregation of Revenue [Line Items]
Regulated Operating Revenue, Other	18,824		79,455
Subsidiaries [Member]
Disaggregation of Revenue [Line Items]
Regulated Operating Revenue, Other	10,069	11,318	28,253	29,356
Total operating revenue	$ 651,464	$ 660,377	$ 2,361,324	$ 2,457,376