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Fair Value Measurements (Tables) | 9 Months Ended
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Sep. 30, 2025
Fair Value Disclosures [Abstract] |
Schedule of Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis | The following table presents the fair value as of September 30, 2025 of our assets and liabilities that are measured at fair value on a recurring basis (dollars in thousands):
| Level 1 |  | Level 2 |  | Level 3 |  | Other |  |  |  | Total
ASSETS |  |  |  |  |  |  |  |  |  |  |
Cash equivalents | $ | 1 |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  |  |  | $ | 1 |
Risk management activities — derivative instruments: |  |  |  |  |  |  |  |  |  |  |
Commodity contracts | — |  |  | 32,443 |  |  | 1,369 |  |  | (11,576) |  |  | (a) |  | 22,236 |
Nuclear decommissioning trusts: |  |  |  |  |  |  |  |  |  |  |
Equity securities | 19,150 |  |  | — |  |  | — |  |  | 2,091 |  |  | (b) |  | 21,241 |
U.S. commingled equity funds | — |  |  | — |  |  | — |  |  | 487,681 |  |  | (c) |  | 487,681 |
U.S. Treasury debt | 352,998 |  |  | — |  |  | — |  |  | — |  |  |  |  | 352,998 |
Corporate debt | — |  |  | 237,191 |  |  | — |  |  | — |  |  |  |  | 237,191 |
Mortgage-backed securities | — |  |  | 232,657 |  |  | — |  |  | — |  |  |  |  | 232,657 |
Municipal bonds | — |  |  | 37,785 |  |  | — |  |  | — |  |  |  |  | 37,785 |
Other fixed income | — |  |  | 23,893 |  |  | — |  |  | — |  |  |  |  | 23,893 |
Subtotal nuclear decommissioning trusts | 372,148 |  |  | 531,526 |  |  | — |  |  | 489,772 |  |  |  |  | 1,393,446 |
Other special use funds: |  |  |  |  |  |  |  |  |  |  |
Equity securities | 103,354 |  |  | — |  |  | — |  |  | 2,167 |  |  | (b) |  | 105,521 |
U.S. Treasury debt | 324,411 |  |  | — |  |  | — |  |  | — |  |  |  |  | 324,411 |
Subtotal other special use funds (d) | 427,765 |  |  | — |  |  | — |  |  | 2,167 |  |  |  |  | 429,932 |
Total assets | $ | 799,914 |  |  | $ | 563,969 |  |  | $ | 1,369 |  |  | $ | 480,363 |  |  |  |  | $ | 1,845,615 |
LIABILITIES |  |  |  |  |  |  |  |  |  |  |
Risk management activities — derivative instruments: |  |  |  |  |  |  |  |  |  |  |
Commodity contracts | $ | — |  |  | $ | (25,218) |  |  | $ | (19,645) |  |  | $ | 5,785 |  |  | (a) |  | $ | (39,078) |
(a)Represents counterparty netting, margin, and collateral. See Note 9. (b)Represents net pending securities sales and purchases. (c)Valued using NAV as a practical expedient and, therefore, are not classified in the fair value hierarchy. (d)All amounts relate to APS, with the exception of $39.4 million related to Pinnacle West’s Captive investments that are classified within Level 1 equity securities. See Note 8. The following table presents the fair value at December 31, 2024 of our assets and liabilities that are measured at fair value on a recurring basis (dollars in thousands):
| Level 1 |  | Level 2 |  | Level 3 |  | Other |  |  |  | Total
ASSETS |  |  |  |  |  |  |  |  |  |  |
Cash equivalents | $ | 23 |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  |  |  | $ | 23 |
Risk management activities — derivative instruments: |  |  |  |  |  |  |  |  |  |  |
Commodity contracts | — |  |  | 13,152 |  |  | 7,176 |  |  | (3,770) |  |  | (a) |  | 16,558 |
Nuclear decommissioning trusts: |  |  |  |  |  |  |  |  |  |  |
Equity securities | 11,859 |  |  | 542 |  |  | — |  |  | 3,335 |  |  | (b) |  | 15,736 |
U.S. commingled equity funds | — |  |  | — |  |  | — |  |  | 423,069 |  |  | (c) |  | 423,069 |
U.S. Treasury debt | 367,396 |  |  | — |  |  | — |  |  | — |  |  |  |  | 367,396 |
Corporate debt | — |  |  | 203,180 |  |  | — |  |  | — |  |  |  |  | 203,180 |
Mortgage-backed securities | — |  |  | 208,533 |  |  | — |  |  | — |  |  |  |  | 208,533 |
Municipal bonds | — |  |  | 37,429 |  |  | — |  |  | — |  |  |  |  | 37,429 |
Other fixed income | — |  |  | 27,502 |  |  | — |  |  | — |  |  |  |  | 27,502 |
Subtotal nuclear decommissioning trusts | 379,255 |  |  | 477,186 |  |  | — |  |  | 426,404 |  |  |  |  | 1,282,845 |
Other special use funds: |  |  |  |  |  |  |  |  |  |  |
Cash equivalents | 25,000 |  |  | — |  |  | — |  |  | — |  |  | (d) |  | 25,000 |
Equity securities | 24,962 |  |  | — |  |  | — |  |  | 2,851 |  |  | (b) (d) |  | 27,813 |
U.S. Treasury debt | 355,544 |  |  | — |  |  | — |  |  | — |  |  |  |  | 355,544 |
Subtotal other special use funds (d) | 405,506 |  |  | — |  |  | — |  |  | 2,851 |  |  |  |  | 408,357 |
Total assets | $ | 784,784 |  |  | $ | 490,338 |  |  | $ | 7,176 |  |  | $ | 425,485 |  |  |  |  | $ | 1,707,783 |
LIABILITIES |  |  |  |  |  |  |  |  |  |  |
Risk management activities — derivative instruments: |  |  |  |  |  |  |  |  |  |  |
Commodity contracts | $ | — |  |  | $ | (40,388) |  |  | $ | (22,215) |  |  | $ | 817 |  |  | (a) |  | $ | (61,786) |
(a)Represents counterparty netting, margin, and collateral. See Note 9. (b)Represents net pending securities sales and purchases. (c)Valued using NAV as a practical expedient and, therefore, are not classified in the fair value hierarchy. (d)All amounts relate to APS, with the exception of $34.2 million related to Pinnacle West’s Captive investments that are classified within Level 1, $25.0 million in cash equivalents and $9.2 million related to equity securities. See Note 8. The following table shows the changes in fair value for our risk management activities’ assets and liabilities that are measured at fair value on a recurring basis using Level 3 inputs (dollars in thousands):
|  | Three Months Ended September 30, |  | Nine Months Ended September 30,
Commodity Contracts |  | 2025 |  | 2024 |  | 2025 |  | 2024
Balance at beginning of period |  | $ | (18,792) |  |  | $ | (21,640) |  |  | $ | (15,039) |  |  | $ | 4,921 |
Total net losses realized/unrealized: |  |  |  |  |  |  |  |
Deferred as a regulatory asset or liability |  | (18,492) |  |  | (25,576) |  |  | (22,121) |  |  | (58,984) |
Settlements |  | 19,283 |  |  | 29,128 |  |  | 18,879 |  |  | 39,076 |
Transfers into Level 3 from Level 2 |  | (275) |  |  | — |  |  | (663) |  |  | (4,565) |
Transfers from Level 3 into Level 2 |  | — |  |  | — |  |  | 668 |  |  | 1,464 |
Balance at end of period |  | $ | (18,276) |  |  | $ | (18,088) |  |  | $ | (18,276) |  |  | $ | (18,088) |
Net unrealized gains/losses included in earnings related to instruments still held at end of period |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |
Schedule of Fair Value Measurement Inputs and Valuation Techniques | The following tables provide information regarding our significant unobservable inputs used to value our risk management derivative Level 3 instruments as of September 30, 2025 and December 31, 2024:
| September 30, 2025 Fair Value (dollars in thousands) |  | Valuation |  | Significant |  |  |  |  |  | Weighted-Average
Commodity Contracts | Assets |  | Liabilities |  | Technique |  | Unobservable Input |  | Range |  | (b)
Electricity Forward Contracts (a) | $ | 1,032 |  |  | $ | 17,576 |  |  | Discounted cash flows |  | Electricity forward price (per megawatt-hour (“MWh”)) |  | $30.85 | - | $157.99 |  | $80.98
Natural Gas Forward Contracts (a) | 337 |  |  | 2,069 |  |  | Discounted cash flows |  | Natural gas forward price (per Million British Thermal Units (“MMBtu”)) |  | $(0.48) | - | $0.10 |  | $(0.09)
Total | $ | 1,369 |  |  | $ | 19,645 |  |  |  |  |  |  |  |  |  |  |
(a)Includes swaps and physical and financial contracts. (b)Unobservable inputs were weighted by the relative fair value of the instrument.
| December 31, 2024 Fair Value (dollars in thousands) |  | Valuation |  | Significant |  |  |  |  |  | Weighted-Average
Commodity Contracts | Assets |  | Liabilities |  | Technique |  | Unobservable Input |  | Range |  | (b)
Electricity Forward Contracts (a) | $ | 708 |  |  | $ | 21,890 |  |  | Discounted cash flows |  | Electricity forward price (per MWh) |  | $ | 25.25 |  | - | $151.11 |  | $106.06
Natural Gas Forward Contracts (a) | 6,468 |  |  | 325 |  |  | Discounted cash flows |  | Natural gas forward price (per MMBtu) |  | $(0.89) | - | $1.47 |  | $0.71
Total | $ | 7,176 |  |  | $ | 22,215 |  |  |  |  |  |  |  |  |  |  |
(a)Includes swaps and physical and financial contracts. (b)Unobservable inputs were weighted by the relative fair value of the instrument.

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- Definition Tabular disclosure of input and valuation technique used to measure fair value and change in valuation approach and technique for each separate class of asset and liability measured on recurring and nonrecurring basis. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (bbb)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 103 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482078/820-10-55-103 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (bbb)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 + Details
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- Definition Tabular disclosure of assets and liabilities, including [financial] instruments measured at fair value that are classified in stockholders' equity, if any, that are measured at fair value on a recurring basis. The disclosures contemplated herein include the fair value measurements at the reporting date by the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 + Details
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