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Regulatory Matters (Tables)
 3 Months Ended
Mar. 31, 2024
Regulated Operations [Abstract]  
Schedule of Capital Structure and Cost of Capital the following proposed capital structure and costs of capital:
Capital StructureCost of Capital
Long-term debt48.07 %3.85 %
Common stock equity51.93 %10.25 %
Weighted-average cost of capital7.17 %
Schedule of Changes in The Deferred Fuel and Purchased Power Regulatory Asset
The following table shows the changes in the deferred fuel and purchased power regulatory asset for 2024 and 2023 (dollars in thousands):
 Three Months Ended
March 31,
 20242023
Beginning balance$463,195 $460,561 
Deferred fuel and purchased power costs — current period33,094 90,305 
Amounts charged to customers(108,552)(80,904)
Ending balance$387,737 $469,962 
Schedule of Regulatory Assets
The detail of regulatory assets is as follows (dollars in thousands): 
 Amortization ThroughMarch 31, 2024December 31, 2023
Pension(a)$686,379 $696,476 
Deferred fuel and purchased power (b) (c)2025387,737 463,195 
Income taxes — allowance for funds used during construction (“AFUDC”) equity2054189,211 189,058 
Deferred fuel and purchased power — mark-to-market (Note 7)
2026154,658 120,214 
Ocotillo deferral2034125,908 128,636 
SCR deferral (e)203887,576 89,477 
Retired power plant costs203379,747 83,536 
Lease incentives(g)54,543 46,615 
Income taxes — investment tax credit basis adjustment205636,017 34,230 
Deferred compensation203633,923 33,972 
Deferred property taxes202730,345 32,488 
Palo Verde VIEs (Note 6)
204620,732 20,772 
Active Union Medical Trust(f)13,809 12,747 
Navajo coal reclamation202610,139 10,883 
Mead-Phoenix transmission line contributions in aid of construction (“CIAC”)20508,633 8,716 
Loss on reacquired debt20387,644 7,965 
Four Corners cost deferral20245,903 7,922 
Tax expense adjustor mechanism (b)20315,026 5,190 
FERC Transmission true up20264,313 616 
Power supply adjustor - interest20253,105 19,416 
OtherVarious4,781 3,912 
Total regulatory assets (d) $1,950,129 $2,016,036 
Less: current regulatory assets$578,869 $625,757 
Total non-current regulatory assets$1,371,260 $1,390,279 

(a)This asset represents the future recovery of pension benefit obligations and expense through retail rates.  If these costs are disallowed by the ACC, this regulatory asset would be charged to OCI and result in lower future revenues.  As a result of the 2019 Rate Case decision, the amount authorized for inclusion in rate base was determined using an averaging methodology, which resulted in a reduced return in retail rates. The 2022 Rate Case decision allows for the full return on the pension asset in rate base. See Note 5 for further discussion.
(b)See “Cost Recovery Mechanisms” discussion above.
(c)Subject to a carrying charge.
(d)There are no regulatory assets for which the ACC has allowed recovery of costs but not allowed a return by exclusion from rate base.  FERC rates are set using a formula rate as described in “Transmission Rates, Transmission Cost Adjustor and Other Transmission Matters.”
(e)See “Four Corners SCR Cost Recovery” discussion above.
(f)Collected in retail rates.
(g)Amortization periods vary based on specific terms of lease contract.
Schedule of Regulatory Liabilities
The detail of regulatory liabilities is as follows (dollars in thousands):
 Amortization ThroughMarch 31, 2024December 31, 2023
Excess deferred income taxes - ACC — Tax Cuts and Jobs Act (a)2046$929,197 $930,344 
Excess deferred income taxes - FERC — Tax Cuts and Jobs Act (a)2058214,466 214,667 
Asset retirement obligations2057411,393 392,383 
Other postretirement benefits(c)215,298 226,726 
Removal costs(d)90,082 94,368 
Income taxes — deferred investment tax credit205668,442 68,521 
Income taxes — change in rates205360,589 60,667 
Four Corners coal reclamation203856,557 55,917 
Renewable energy standard (b)202451,001 43,251 
Spent nuclear fuel202731,552 33,154 
Demand side management (b)202420,905 14,374 
Sundance maintenance203120,763 19,989 
Property tax deferral20279,541 10,850 
Tax expense adjustor mechanism (b)20324,796 4,835 
FERC transmission true up (b)2026— 1,869 
OtherVarious3,090 3,873 
Total regulatory liabilities $2,187,672 $2,175,788 
Less: current regulatory liabilities$221,552 $209,923 
Total non-current regulatory liabilities$1,966,120 $1,965,865 

(a)For purposes of presentation on the Statement of Cash Flows, amortization of the regulatory liabilities for excess deferred income taxes are reflected as “Deferred income taxes” under Cash Flows From Operating Activities.
(b)See “Cost Recovery Mechanisms” discussion above.
(c)See Note 5.
(d)In accordance with regulatory accounting, APS accrues removal costs for its regulated assets, even if there is no legal obligation for removal.