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Regulatory Matters (Tables) | 12 Months Ended
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Dec. 31, 2018
Regulated Operations [Abstract] |
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 (liability) for 2018 and 2017 (dollars in thousands):
| Twelve Months Ended December 31,
| 2018 |  | 2017
Beginning balance | $ | 75,637 |  |  | $ | 12,465 |
Deferred fuel and purchased power costs — current period | 78,277 |  |  | 48,405 |
Amounts refunded/(charged) to customers | (116,750 | ) |  | 14,767 |
Ending balance | $ | 37,164 |  |  | $ | 75,637 |
Schedule of regulatory assets | The detail of regulatory assets is as follows (dollars in thousands):
S |  |  | December 31, 2018 |  | December 31, 2017
| Amortization Through |  | Current |  | Non-Current |  | Current |  | Non-Current
Pension | (a) |  | $ | — |  |  | $ | 733,351 |  |  | $ | — |  |  | $ | 576,188 |
Retired power plant costs | 2033 |  | 28,182 |  |  | 167,164 |  |  | 27,402 |  |  | 188,843 |
Income taxes - AFUDC equity | 2048 |  | 6,457 |  |  | 151,467 |  |  | 3,828 |  |  | 142,852 |
Deferred fuel and purchased power — mark-to-market (Note 16) | 2023 |  | 31,728 |  |  | 23,768 |  |  | 52,100 |  |  | 34,845 |
Deferred fuel and purchased power (b) (c) | 2019 |  | 37,164 |  |  | — |  |  | 75,637 |  |  | — |
Four Corners cost deferral | 2024 |  | 8,077 |  |  | 40,228 |  |  | 8,077 |  |  | 48,305 |
Income taxes — investment tax credit basis adjustment | 2047 |  | 1,079 |  |  | 25,522 |  |  | 1,066 |  |  | 26,218 |
Lost fixed cost recovery (b) | 2019 |  | 32,435 |  |  | — |  |  | 59,844 |  |  | — |
Palo Verde VIEs (Note 18) | 2046 |  | — |  |  | 20,015 |  |  | — |  |  | 19,395 |
Deferred compensation | 2036 |  | — |  |  | 36,523 |  |  | — |  |  | 36,413 |
Deferred property taxes | 2027 |  | 8,569 |  |  | 66,356 |  |  | 8,569 |  |  | 74,926 |
Loss on reacquired debt | 2038 |  | 1,637 |  |  | 13,668 |  |  | 1,637 |  |  | 15,305 |
Tax expense of Medicare subsidy | 2024 |  | 1,235 |  |  | 6,176 |  |  | 1,236 |  |  | 7,415 |
TCA balancing account (b) | 2020 |  | 3,860 |  |  | 772 |  |  | 1,220 |  |  | — |
AG-1 deferral | 2022 |  | 2,654 |  |  | 5,819 |  |  | 2,654 |  |  | 8,472 |
Mead-Phoenix transmission line CIAC | 2050 |  | 332 |  |  | 10,044 |  |  | 332 |  |  | 10,376 |
Coal reclamation | 2026 |  | 1,546 |  |  | 15,607 |  |  | 1,068 |  |  | 12,396 |
SCR deferral | N/A |  | — |  |  | 23,276 |  |  | — |  |  | 353 |
Other | Various |  | 1,947 |  |  | 3,185 |  |  | 3,418 |  |  | — |
Total regulatory assets (d) |  |  | $ | 166,902 |  |  | $ | 1,342,941 |  |  | $ | 248,088 |  |  | $ | 1,202,302 |
(a) | This asset represents the future recovery of pension benefit obligations 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. See Note 7 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.”
Schedule of regulatory liabilities | The detail of regulatory liabilities is as follows (dollars in thousands):
|  |  | December 31, 2018 |  | December 31, 2017
| Amortization Through |  | Current |  | Non-Current |  | Current |  | Non-Current
Excess deferred income taxes - ACC - Tax Cuts and Jobs Act | (a) |  | $ | — |  |  | $ | 1,272,709 |  |  | $ | — |  |  | $ | 1,266,104 |
Excess deferred income taxes - FERC - Tax Cuts and Jobs Act | 2058 |  | 6,302 |  |  | 243,691 |  |  | — |  |  | 254,170 |
Asset retirement obligations | 2057 |  | — |  |  | 278,585 |  |  | — |  |  | 332,171 |
Removal costs | (b) |  | 39,866 |  |  | 177,533 |  |  | 18,238 |  |  | 209,191 |
Other post retirement benefits | (c) |  | 37,864 |  |  | 125,903 |  |  | 37,642 |  |  | 151,985 |
Income taxes - deferred investment tax credit | 2047 |  | 2,164 |  |  | 51,120 |  |  | 2,164 |  |  | 52,497 |
Income taxes - change in rates | 2048 |  | 2,769 |  |  | 70,069 |  |  | 2,573 |  |  | 70,537 |
Spent nuclear fuel | 2027 |  | 6,503 |  |  | 57,002 |  |  | 6,924 |  |  | 62,132 |
Renewable energy standard (d) | 2020 |  | 44,966 |  |  | 20 |  |  | 23,155 |  |  | — |
Demand side management (d) | 2020 |  | 14,604 |  |  | 4,123 |  |  | 3,066 |  |  | 4,921 |
Sundance maintenance | 2030 |  | 1,278 |  |  | 17,228 |  |  | — |  |  | 16,897 |
Deferred gains on utility property | 2022 |  | 4,423 |  |  | 6,581 |  |  | 4,423 |  |  | 10,988 |
Four Corners coal reclamation | 2038 |  | 1,858 |  |  | 17,871 |  |  | 1,858 |  |  | 18,921 |
Tax expense adjustor mechanism (d) | 2019 |  | 3,237 |  |  | — |  |  | — |  |  | — |
Other | Various |  | 42 |  |  | 3,541 |  |  | 43 |  |  | 2,022 |
Total regulatory liabilities |  |  | $ | 165,876 |  |  | $ | 2,325,976 |  |  | $ | 100,086 |  |  | $ | 2,452,536 |
(a) | While the majority of the excess deferred tax balance shown is subject to special amortization rules under federal income tax laws, which require amortization of the balance over the remaining regulatory life of the related property, treatment of a portion of the liability, and the month in which pass-through of the excess deferred tax balance will begin is subject to regulatory approval. This approval will be sought through the Company's TEAM adjustor mechanism. As a result, the Company cannot estimate the amount of this regulatory liability which is expected to reverse within the next 12 months. See Note 4.
(b) | In accordance with regulatory accounting guidance, APS accrues for removal costs for its regulated assets, even if there is no legal obligation for removal.
(c) | See Note 7.
(d) | See “Cost Recovery Mechanisms” discussion above.

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- Definition Tabular disclosure of assets that are created when regulatory agencies permit public utilities to defer certain costs included in rate-setting to the balance sheet. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 715 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501251&loc=d3e52485-110419 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44264-110382 + Details
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