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, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Nuclear decommissioning trust fund assets
Fair Value	$ 1,687,511		$ 1,687,511		$ 1,564,027
Total Unrealized Gains			382,693		358,112
Total Unrealized Losses			(22,091)		(40,868)
Amortized cost	1,193,419		1,193,419		1,120,000
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds
Realized gains	3,825	$ 34,897	67,340	$ 71,338
Realized losses	(4,162)	(12,115)	(10,683)	(29,001)
Proceeds from the sale of securities	367,996	578,140	1,140,371	1,145,668
Nuclear Decommissioning Trusts
Nuclear decommissioning trust fund assets
Fair Value	1,300,012		1,300,012		1,201,246
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds
Realized gains	3,825	34,897	67,260	71,338
Realized losses	(4,162)	(11,568)	(10,683)	(28,454)
Proceeds from the sale of securities	293,758	487,324	942,211	922,270
Other Special Use Funds
Nuclear decommissioning trust fund assets
Fair Value	387,499		387,499		362,781
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds
Realized gains	0	0	80	0
Realized losses	0	(547)	0	(547)
Proceeds from the sale of securities	74,238	$ 90,816	198,160	$ 223,398
Equity securities
Nuclear decommissioning trust fund assets
Equity securities	484,193		484,193		461,671
Total Unrealized Gains			353,327		336,555
Total Unrealized Losses			0		0
Equity securities | Nuclear Decommissioning Trusts
Nuclear decommissioning trust fund assets
Equity securities	430,217		430,217		420,680
Equity securities | Other Special Use Funds
Nuclear decommissioning trust fund assets
Equity securities	53,976		53,976		40,991
Available for sale-fixed income securities
Nuclear decommissioning trust fund assets
Fair Value	1,199,950		1,199,950		1,100,927
Total Unrealized Gains			28,894		21,518
Total Unrealized Losses			(22,091)		(40,868)
Fair value of fixed income securities, summarized by contractual maturities
Less than one year	169,443		169,443
1 year – 5 years	461,876		461,876
5 years – 10 years	197,500		197,500
Greater than 10 years	371,131		371,131
Total	1,199,950		1,199,950
Available for sale-fixed income securities | Nuclear Decommissioning Trusts
Nuclear decommissioning trust fund assets
Fair Value	868,187		868,187		781,333
Fair value of fixed income securities, summarized by contractual maturities
Less than one year	30,015		30,015
1 year – 5 years	269,541		269,541
5 years – 10 years	197,500		197,500
Greater than 10 years	371,131		371,131
Total	868,187		868,187
Available for sale-fixed income securities | Other Special Use Funds
Nuclear decommissioning trust fund assets
Fair Value	331,763		331,763		319,594
Available for sale-fixed income securities | Coal Reclamation Escrow Account
Fair value of fixed income securities, summarized by contractual maturities
Less than one year	62,874		62,874
1 year – 5 years	48,840		48,840
5 years – 10 years	0		0
Greater than 10 years	0		0
Total	111,714		111,714
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	76,554		76,554
1 year – 5 years	143,495		143,495
5 years – 10 years	0		0
Greater than 10 years	0		0
Total	220,049		220,049
Other
Nuclear decommissioning trust fund assets
Fair Value	3,368		3,368		1,429
Total Unrealized Gains			472		39
Total Unrealized Losses			0		0
Other | Nuclear Decommissioning Trusts
Nuclear decommissioning trust fund assets
Fair Value	1,608		1,608		(767)
Other | Other Special Use Funds
Nuclear decommissioning trust fund assets
Fair Value	$ 1,760		$ 1,760		$ 2,196