Regulatory Matters - Regulatory Matters - COVID-19 (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Oct. 21, 2020	May 05, 2020
Public Utilities, General Disclosures [Line Items]
Pre-tax income	$ 428,479,000	$ 370,415,000	$ 682,656,000	$ 561,723,000
APS
Public Utilities, General Disclosures [Line Items]
Pre-tax income	437,097,000	$ 379,897,000	703,536,000	$ 588,012,000
Demand side management funds						$ 36,000,000
Customer credits	43,000,000		43,000,000
Customer credits, additional funds	7,000,000		7,000,000
Voluntary funds	8,000,000		8,000,000			5,300,000
Customer COVID assistance	$ 6,800,000		$ 6,800,000
Customer support fund						1,500,000
Customer support fund, bill credit						100
COVID bill credit						100
Customer assistance, small customers, bill credit						$ 1,000
APS | Subsequent Event
Public Utilities, General Disclosures [Line Items]
COVID, support					$ 4,300,000
Customer support fund, non-profits and community organizations					$ 1,250,000