Investments in Nuclear Decommissioning Trusts and Other Special Use Funds (Details) - APS - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2022	Dec. 31, 2023
Nuclear decommissioning trust fund assets
Fair Value	$ 1,603,249			$ 1,564,027
Total Unrealized Gains	337,321		$ 358,112
Total Unrealized Losses	(48,075)		(40,868)
Amortized cost	1,194,000			1,120,000
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds
Realized gains	54,572	$ 1,210
Realized losses	(2,815)	(5,694)
Proceeds from the sale of securities	443,870	226,626
Nuclear Decommissioning Trusts
Nuclear decommissioning trust fund assets
Fair Value	1,239,024			1,201,246
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds
Realized gains	54,492	1,210
Realized losses	(2,815)	(5,694)
Proceeds from the sale of securities	377,822	136,185
Other Special Use Funds
Nuclear decommissioning trust fund assets
Fair Value	364,225			362,781
Realized gains and losses and proceeds from the sale of securities by the nuclear decommissioning trust funds
Realized gains	80	0
Realized losses	0	0
Proceeds from the sale of securities	66,048	$ 90,441
Equity securities
Nuclear decommissioning trust fund assets
Equity securities	440,942			461,671
Total Unrealized Gains	325,101		336,555
Total Unrealized Losses	0		0
Equity securities | Nuclear Decommissioning Trusts
Nuclear decommissioning trust fund assets
Equity securities	394,277			420,680
Equity securities | Other Special Use Funds
Nuclear decommissioning trust fund assets
Equity securities	46,665			40,991
Available for sale-fixed income securities
Nuclear decommissioning trust fund assets
Fair Value	1,158,755			1,100,927
Total Unrealized Gains	12,056		21,518
Total Unrealized Losses	(48,075)		(40,868)
Fair value of fixed income securities, summarized by contractual maturities
Less than one year	120,322
1 year – 5 years	449,774
5 years – 10 years	218,770
Greater than 10 years	369,889
Total	1,158,755
Available for sale-fixed income securities | Nuclear Decommissioning Trusts
Nuclear decommissioning trust fund assets
Fair Value	842,618			781,333
Fair value of fixed income securities, summarized by contractual maturities
Less than one year	24,043
1 year – 5 years	254,711
5 years – 10 years	193,975
Greater than 10 years	369,889
Total	842,618
Available for sale-fixed income securities | Other Special Use Funds
Nuclear decommissioning trust fund assets
Fair Value	316,137			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	59,198
1 year – 5 years	43,219
5 years – 10 years	0
Greater than 10 years	0
Total	102,417
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	37,081
1 year – 5 years	151,844
5 years – 10 years	24,795
Greater than 10 years	0
Total	213,720
Other
Nuclear decommissioning trust fund assets
Fair Value	3,552			1,429
Total Unrealized Gains	164		39
Total Unrealized Losses	0		$ 0
Other | Nuclear Decommissioning Trusts
Nuclear decommissioning trust fund assets
Fair Value	2,129			(767)
Other | Other Special Use Funds
Nuclear decommissioning trust fund assets
Fair Value	$ 1,423			$ 2,196