Utility Plant, Palo Verde and Other Jointly-Owned Utility Plant Significant Accounting Policies (Policies)	12 Months Ended
Dec. 31, 2015
Accounting Policies [Abstract]
Depreciation, Depletion, and Amortization	Amortization of intangible plant (software) is provided on a straight-line basis over the estimated useful life of the asset (ranging from 3 to 15 years).

Disclosure of accounting policy for depreciation, depletion, and amortization of property and equipment costs, including methods used and estimated useful lives and how impairment of such assets is assessed and recognized.

No definition available.

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