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Summary of Significant Accounting Policies - Summary of Property, Plant and Equipment (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Utility Plant and Depreciation [Line Items] |  |
Net | $ 11,669,526 | $ 11,371,788
Construction work in progress | 1,291,498 | 1,019,947
Palo Verde sale leaseback, net of accumulated depreciation | 109,645 | 113,515
Intangible assets, net of accumulated amortization | 257,189 | 90,022
Nuclear fuel, net of accumulated amortization | 117,408 | 119,004
Total property, plant and equipment | 13,445,266 | 12,714,276
Electric Service |  |
Utility Plant and Depreciation [Line Items] |  |
Generation | 7,963,998 | 7,874,898
Transmission | 2,836,578 | 2,746,508
Distribution | 6,025,856 | 5,738,801
General plant | 971,629 | 981,681
Plant in service and held for future use | 17,798,061 | 17,341,888
Accumulated depreciation and amortization | (6,128,535) | (5,970,100)
Net | 11,669,526 | 11,371,788
Construction work in progress | 1,291,498 | 1,019,947
Palo Verde sale leaseback, net of accumulated depreciation | 109,645 | 113,515
Intangible assets, net of accumulated amortization | 257,189 | 90,022
Nuclear fuel, net of accumulated amortization | 117,408 | 119,004
Total property, plant and equipment | $ 13,445,266 | $ 12,714,276

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