Revenue - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Operating revenues	$ 3,586,982	$ 3,471,209	$ 3,691,247
Regulatory cost recovery revenue	54,000	56,000	47,000
Electric and Transmission Service
Disaggregation of Revenue [Line Items]
Operating revenues	3,533,000	3,415,000	3,644,000
Retail Electric Service | Retail residential
Disaggregation of Revenue [Line Items]
Operating revenues	1,929,178	$ 1,761,122	$ 1,867,370
Retail Electric Service | Arizona Attorney General Settlement | Retail residential
Disaggregation of Revenue [Line Items]
Operating revenues	$ (24,000)