Investments in Nuclear Decommissioning Trusts and Other Special Use Funds (Details) - APS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Nuclear decommissioning trust fund assets
Fair Value	$ 1,488,622		$ 1,488,622		$ 1,420,641
Total Unrealized Gains			328,510		337,994
Total Unrealized Losses			(74,406)		(69,091)
Amortized cost	1,079,000		1,079,000		927,000
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds
Realized gains	34,897	$ 788	71,338	$ 8,093
Realized losses	(12,115)	(6,908)	(29,001)	(26,582)
Proceeds from the sale of securities	578,140	218,817	1,145,668	910,487
Nuclear Decommissioning Trusts
Nuclear decommissioning trust fund assets
Fair Value	1,120,463		1,120,463		1,073,410
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds
Realized gains	34,897	788	71,338	8,093
Realized losses	(11,568)	(6,908)	(28,454)	(26,582)
Proceeds from the sale of securities	487,324	153,573	922,270	783,232
Other Special Use Funds
Nuclear decommissioning trust fund assets
Fair Value	368,159		368,159		347,231
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds
Realized gains	0	0	0	0
Realized losses	(547)	0	(547)	0
Proceeds from the sale of securities	90,816	$ 65,244	223,398	$ 127,255
Equity securities
Nuclear decommissioning trust fund assets
Equity securities	499,316		499,316		554,214
Total Unrealized Gains			327,887		334,817
Total Unrealized Losses			(23)		(267)
Equity securities | Nuclear Decommissioning Trusts
Nuclear decommissioning trust fund assets
Equity securities	444,063		444,063		487,240
Equity securities | Other Special Use Funds
Nuclear decommissioning trust fund assets
Equity securities	55,253		55,253		66,974
Available for sale-fixed income securities
Nuclear decommissioning trust fund assets
Fair Value	1,005,134		1,005,134		861,637
Total Unrealized Gains			623		3,177
Total Unrealized Losses			(74,383)		(68,795)
Fair value of fixed income securities, summarized by contractual maturities
Less than one year	96,094		96,094
1 year – 5 years	421,465		421,465
5 years – 10 years	166,450		166,450
Greater than 10 years	321,125		321,125
Total	1,005,134		1,005,134
Available for sale-fixed income securities | Nuclear Decommissioning Trusts
Nuclear decommissioning trust fund assets
Fair Value	693,510		693,510		582,343
Fair value of fixed income securities, summarized by contractual maturities
Less than one year	18,012		18,012
1 year – 5 years	194,625		194,625
5 years – 10 years	163,662		163,662
Greater than 10 years	317,211		317,211
Total	693,510		693,510
Available for sale-fixed income securities | Other Special Use Funds
Nuclear decommissioning trust fund assets
Fair Value	311,624		311,624		279,294
Available for sale-fixed income securities | Coal Reclamation Escrow Account
Fair value of fixed income securities, summarized by contractual maturities
Less than one year	59,191		59,191
1 year – 5 years	42,158		42,158
5 years – 10 years	0		0
Greater than 10 years	3,914		3,914
Total	105,263		105,263
Available for sale-fixed income securities | Active Union Employee Medical Account
Fair value of fixed income securities, summarized by contractual maturities
Less than one year	18,891		18,891
1 year – 5 years	184,682		184,682
5 years – 10 years	2,788		2,788
Greater than 10 years	0		0
Total	206,361		206,361
Other
Nuclear decommissioning trust fund assets
Fair Value	(15,828)		(15,828)		4,790
Total Unrealized Gains			0		0
Total Unrealized Losses			0		(29)
Other | Nuclear Decommissioning Trusts
Nuclear decommissioning trust fund assets
Fair Value	(17,110)		(17,110)		3,827
Other | Other Special Use Funds
Nuclear decommissioning trust fund assets
Fair Value	$ 1,282		$ 1,282		$ 963