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Jointly-Owned Facilities (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Jul. 06, 2016
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4CA |  |
Interests in jointly-owned facilities |  |
Plant in Service | $ 141,000 |
Accumulated Depreciation | 83,000 |
Construction work in progress | $ 25,000 |
Palo Verde Units 1 and 3 | ARIZONA PUBLIC SERVICE COMPANY |  |
Interests in jointly-owned facilities |  |
Percent Owned | 29.10% |
Plant in Service | $ 1,872,104 |
Accumulated Depreciation | 1,092,049 |
Construction work in progress | $ 24,257 |
Palo Verde Unit 2 | ARIZONA PUBLIC SERVICE COMPANY |  |
Interests in jointly-owned facilities |  |
Percent Owned | 16.80% |
Plant in Service | $ 619,263 |
Accumulated Depreciation | 364,516 |
Construction work in progress | $ 14,672 |
Palo Verde Common | ARIZONA PUBLIC SERVICE COMPANY |  |
Interests in jointly-owned facilities |  |
Percent Owned | 28.00% |
Plant in Service | $ 726,223 |
Accumulated Depreciation | 262,065 |
Construction work in progress | 46,577 |
Palo Verde Sale Leaseback | ARIZONA PUBLIC SERVICE COMPANY |  |
Interests in jointly-owned facilities |  |
Plant in Service | 351,050 |
Accumulated Depreciation | 241,405 |
Construction work in progress | $ 0 |
Four Corners Generating Station | ARIZONA PUBLIC SERVICE COMPANY |  |
Interests in jointly-owned facilities |  |
Percent Owned | 63.00% |
Plant in Service | $ 1,196,683 |
Accumulated Depreciation | 568,304 |
Construction work in progress | $ 240,514 |
Cholla Common Facilities | ARIZONA PUBLIC SERVICE COMPANY |  |
Interests in jointly-owned facilities |  |
Percent Owned | 50.50% |
Plant in Service | $ 180,907 |
Accumulated Depreciation | 69,633 |
Construction work in progress | $ 1,091 |
ANPP 500kV System | ARIZONA PUBLIC SERVICE COMPANY |  |
Interests in jointly-owned facilities |  |
Percent Owned | 34.00% |
Plant in Service | $ 130,767 |
Accumulated Depreciation | 46,400 |
Construction work in progress | $ 684 |
Navajo Southern System | ARIZONA PUBLIC SERVICE COMPANY |  |
Interests in jointly-owned facilities |  |
Percent Owned | 27.50% |
Plant in Service | $ 85,299 |
Accumulated Depreciation | 28,915 |
Construction work in progress | $ 180 |
Palo Verde — Yuma 500kV System | ARIZONA PUBLIC SERVICE COMPANY |  |
Interests in jointly-owned facilities |  |
Percent Owned | 18.10% |
Plant in Service | $ 14,765 |
Accumulated Depreciation | 6,614 |
Construction work in progress | $ 486 |
Four Corners Switchyards | ARIZONA PUBLIC SERVICE COMPANY |  |
Interests in jointly-owned facilities |  |
Percent Owned | 63.20% |
Plant in Service | $ 66,386 |
Accumulated Depreciation | 12,605 |
Construction work in progress | $ 327 |
Phoenix — Mead System | ARIZONA PUBLIC SERVICE COMPANY |  |
Interests in jointly-owned facilities |  |
Percent Owned | 17.10% |
Plant in Service | $ 39,383 |
Accumulated Depreciation | 17,600 |
Construction work in progress | $ 41 |
Palo Verde — Rudd 500kV System | ARIZONA PUBLIC SERVICE COMPANY |  |
Interests in jointly-owned facilities |  |
Percent Owned | 50.00% |
Plant in Service | $ 97,600 |
Accumulated Depreciation | 23,884 |
Construction work in progress | $ 245 |
Morgan — Pinnacle Peak System | ARIZONA PUBLIC SERVICE COMPANY |  |
Interests in jointly-owned facilities |  |
Percent Owned | 64.60% |
Plant in Service | $ 117,721 |
Accumulated Depreciation | 14,569 |
Construction work in progress | $ 1 |
Round Valley System | ARIZONA PUBLIC SERVICE COMPANY |  |
Interests in jointly-owned facilities |  |
Percent Owned | 50.00% |
Plant in Service | $ 515 |
Accumulated Depreciation | 141 |
Construction work in progress | $ 0 |
Palo Verde — Morgan System | ARIZONA PUBLIC SERVICE COMPANY |  |
Interests in jointly-owned facilities |  |
Percent Owned | 90.90% |
Plant in Service | $ 137,887 |
Accumulated Depreciation | 3,948 |
Construction work in progress | $ 94,350 |
Hassayampa — North Gila System | ARIZONA PUBLIC SERVICE COMPANY |  |
Interests in jointly-owned facilities |  |
Percent Owned | 80.00% |
Plant in Service | $ 142,541 |
Accumulated Depreciation | 6,953 |
Construction work in progress | $ 0 |
Cholla 500kV Switchyard | ARIZONA PUBLIC SERVICE COMPANY |  |
Interests in jointly-owned facilities |  |
Percent Owned | 85.70% |
Plant in Service | $ 5,243 |
Accumulated Depreciation | 1,312 |
Construction work in progress | $ 190 |
Saguaro 500kV Switchyard | ARIZONA PUBLIC SERVICE COMPANY |  |
Interests in jointly-owned facilities |  |
Percent Owned | 60.00% |
Plant in Service | $ 20,473 |
Accumulated Depreciation | 12,574 |
Construction work in progress | $ 0 |
Kyrene - Knox System | ARIZONA PUBLIC SERVICE COMPANY |  |
Interests in jointly-owned facilities |  |
Percent Owned | 50.00% |
Plant in Service | $ 578 |
Accumulated Depreciation | 297 |
Construction work in progress | $ 0 |
Navajo Plant | ARIZONA PUBLIC SERVICE COMPANY |  |
Interests in jointly-owned facilities |  |
Ownership interest by noncontrolling owners (as a percent) | 14.00% |
El Paso's Interest in Four Corners | 4CA |  |
Interests in jointly-owned facilities |  |
Ownership interest acquired (as a percent) | 7.00% | 7.00%

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