New Accounting Standards New Accounting Standards (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2018
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Reclassification of income tax effect related to tax reform	$ 0
Accounting Standards Update 2017-07
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net periodic benefit cost (credit)	(4,000)
Accounting Standards Update 2017-07 | Scenario, Forecast
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net periodic benefit cost (credit)		$ (15,000)
Accounting Standards Update 2018-02
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Reclassification of income tax effect related to tax reform	9,000
Accounting Standards Update 2018-02 | Arizona Public Service Company
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Reclassification of income tax effect related to tax reform	$ 5,000