Regulatory Matters Regulatory Matters - COVID-19 (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2020	May 05, 2020
Public Utilities, General Disclosures [Line Items]
Pre-tax income	$ 239,520,000	$ 166,099,000	$ 254,177,000	$ 191,308,000
Customer support, not yet assigned	3,000,000		3,000,000
APS
Public Utilities, General Disclosures [Line Items]
Pre-tax income	245,669,000	$ 173,513,000	266,439,000	$ 208,115,000
Customer support fund						$ 1,500,000
Customer support fund, bill credit						100
Demand side management funds						36,000,000
Customer credits	40,000,000		40,000,000
Customer credits, additional funds	4,000,000		4,000,000
Voluntary funds	$ 8,000,000		$ 8,000,000			5,300,000
Customer assistance, small customers						2,300,000
Customer assistance, small customers, bill credit						1,000
Customer support fund, non-profits and community organizations						$ 1,250,000
Minimum | Damage from Fire, Explosion or Other Hazard | Forecast | APS
Public Utilities, General Disclosures [Line Items]
Pre-tax income					$ 20,000,000
Maximum | Damage from Fire, Explosion or Other Hazard | Forecast | APS
Public Utilities, General Disclosures [Line Items]
Pre-tax income					$ 30,000,000