Regulatory Matters - Cost Recovery Mechanisms (Details)																												1 Months Ended		6 Months Ended		12 Months Ended
	Nov. 01, 2021 $ / kWh	Oct. 01, 2021 $ / kWh	Jun. 07, 2021 USD ($)	Jun. 01, 2021 USD ($)	Apr. 01, 2021 $ / kWh	Feb. 22, 2021 USD ($)	Feb. 15, 2021 USD ($)	Feb. 01, 2021 USD ($) $ / kWh	Aug. 20, 2020 USD ($) Customer	Jun. 01, 2020 USD ($)	May 01, 2020 $ / kWh	Feb. 14, 2020 USD ($)	Feb. 01, 2020 $ / kWh	Nov. 14, 2019 USD ($) Customer	Oct. 31, 2019 USD ($)	Oct. 29, 2019 USD ($)	Jun. 01, 2019 USD ($)	May 01, 2019 $ / kWh	Apr. 10, 2019	Feb. 15, 2019 USD ($)	Feb. 01, 2019 $ / kWh	Aug. 13, 2018 USD ($)	Feb. 15, 2018 USD ($)	Feb. 01, 2018 $ / kWh	Jan. 08, 2018 USD ($)	Nov. 20, 2017 USD ($)	Sep. 01, 2017 USD ($) $ / kWh	Mar. 31, 2021	Feb. 28, 2021	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) program MW	Dec. 31, 2017 $ / kWh	Jul. 01, 2021 USD ($)	Jul. 01, 2020 USD ($)	May 15, 2020 USD ($)	May 05, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jul. 01, 2019 USD ($)	Mar. 15, 2019 agreement	Dec. 31, 2018 USD ($)	Nov. 14, 2017 USD ($)
Change in regulatory asset
Deferred fuel and purchased power costs — current period																														$ 135,905,000	$ 26,473,000
Amounts (charged) refunded to customers																														(10,828,000)	4,815,000
Rate plan comparison tool, number of customers | Customer									3,800					13,000
Rate plan comparison tool, inconvenience payment									$ 25					$ 25
APS
Change in regulatory asset
Deferred fuel and purchased power costs — current period																														135,905,000	26,473,000
Amounts (charged) refunded to customers																														(10,828,000)	4,815,000
Percentage increase under PSA effective for first billing cycle beginning April 2021																												50.00%	50.00%
Remaining percentage increase under PSA effective for first billing cycle beginning November 2021																												50.00%	50.00%
Demand side management funds																																					$ 36,000,000
Customer credits																														43,000,000
Customer credits, additional funds																														$ 7,000,000
APS | 2017 Settlement Agreement and its Customer Education and Outreach Plan
Change in regulatory asset
Settlement amount						$ 24,750,000
Settlement amount returned to customers						$ 24,000,000
Lost Fixed Cost Recovery Mechanisms | APS
Change in regulatory asset
Fixed cost recoverable per power lost (in dollars per kWh) | $ / kWh																																	0.025
Percentage of retail revenues																														1.00%
Amount of adjustment representing prorated sales losses pending approval							$ 38,500,000					$ 26,600,000								$ 36,200,000			$ 60,700,000
Increase (decrease) in amount of adjustment representing prorated sales losses							$ 11,800,000					$ (9,600,000)								$ (24,500,000)
ACC | APS
Settlement Agreement
Program term																																18 years
Change in regulatory asset
Gross-up for revenue requirement of rate regulation															$ (184,000,000)							$ 86,500,000			$ 119,100,000
Deferred taxes amortization, period																			28 years 6 months
Public Utilities, one-time bill credit																$ 64,000,000
Public Utilities, one-time bill credit, additional benefit																$ 39,500,000
Number of programs | program																																2
Solar power capacity (in MW) | MW																																80
ACC | RES | APS
Settlement Agreement
Plan term																														5 years
ACC | RES 2018 | APS
Settlement Agreement
Amount of proposed budget																																		$ 93,100,000	$ 84,700,000				$ 86,300,000
Revenue requirements																																			$ 4,500,000
Authorized amount to be collected			$ 68,300,000
ACC | RES 2018 | APS | Solar Communities
Settlement Agreement
Program term																										3 years
ACC | Demand Side Management Adjustor Charge 2018 | APS
Settlement Agreement
Amount of proposed budget																											$ 52,600,000															$ 52,600,000
ACC | Demand Side Management Adjustor Charge 2019 | APS
Settlement Agreement
Amount of proposed budget																																									$ 34,100,000
ACC | Demand Side Management Adjustor Charge 2020 | APS
Settlement Agreement
Amount of proposed budget																																				$ 51,900,000		$ 51,900,000
ACC | Power Supply Adjustor (PSA) | APS
Change in regulatory asset
Beginning balance																														$ 175,835,000	70,137,000	$ 70,137,000
Deferred fuel and purchased power costs — current period																														135,905,000	26,473,000
Amounts (charged) refunded to customers																														(10,828,000)	4,815,000
Ending balance																														$ 300,912,000	$ 101,425,000	175,835,000
PSA rate (in dollars per kWh) | $ / kWh					0.001544			0.003544					(0.000456)								0.001658			0.004555
PSA rate for prior year (in dollars per kWh) | $ / kWh					(0.004444)			0.003434					(0.002086)								0.000536
Forward component of increase in PSA (in dollars per kWh) | $ / kWh					0.005988			0.000110					0.001630								0.001122
Fuel and purchased power costs above annual cap								$ 215,900,000
ACC | Net Metering | APS
Change in regulatory asset
Cost of service, resource comparison proxy method, maximum annual percentage decrease																											10.00%
Cost of service for interconnected DG system customers, grandfathered period																											20 years
Cost of service for new customers, guaranteed export price period																											10 years
First-year export energy price (in dollars per kWh) | $ / kWh																											0.129
Second-year export energy price (in dollars per kWh) | $ / kWh											0.094							0.105
ACC | Demand Side Management Adjustor Charge 2021 | APS
Settlement Agreement
Amount of proposed budget																																$ 63,700,000
FERC | Environmental Improvement Surcharge | APS
Change in regulatory asset
Increase (decrease) in annual wholesale transmission rates								10,300,000
Rate matters, increase (decrease) in cost recovery, excess of annual amount								$ 1,500,000
FERC | Open Access Transmission Tariff | APS
Change in regulatory asset
Increase (decrease) in annual wholesale transmission rates				$ 4,000,000						$ (6,100,000)							$ 25,800,000
Increase (decrease) in wholesale customer rates				(3,200,000)						4,800,000							21,100,000
Increase (decrease) in retail customer rates				7,200,000						(10,900,000)							4,700,000
Increase (decrease) in retail revenue requirements				$ (28,400,000)						$ (7,400,000)							$ 4,900,000
Cost Recovery Mechanisms | ACC | Power Supply Adjustor (PSA) | APS
Change in regulatory asset
Historical component of increase in PSA (in dollars per kWh) | $ / kWh								0.004					(0.002115)								(0.002897)
Cost recovery, number of agreements | agreement																																								2
Forecast | ACC | Power Supply Adjustor (PSA) | APS
Change in regulatory asset
PSA rate (in dollars per kWh) | $ / kWh	0.003544
PSA rate for prior year (in dollars per kWh) | $ / kWh	(0.004444)
Forward component of increase in PSA (in dollars per kWh) | $ / kWh	0.007988
Forecast | ACC | Net Metering | APS
Change in regulatory asset
Second-year export energy price (in dollars per kWh) | $ / kWh		0.105
Minimum | ACC | APS
Change in regulatory asset
Operating results															$ (69,000,000)
Minimum | ACC | RES 2018 | APS | Solar Communities
Settlement Agreement
Required annual capital investment																										$ 10,000,000
Maximum | ACC | RES 2018 | APS | Solar Communities
Settlement Agreement
Required annual capital investment																										$ 15,000,000