Utility Plant, Palo Verde and Other Jointly-Owned Utility Plant (Depreciable Assets By Each Major Class) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment and Finite-Lived Intangible Assets [Line Items]
Gross Plant	$ 3,076,549	$ 2,857,913
Accumulated Depreciation	(1,214,088)	(1,162,483)
Net plant in service	1,862,461
Intangible Plant Software
Property, Plant and Equipment and Finite-Lived Intangible Assets [Line Items]
Gross Plant	69,661
Accumulated Depreciation	(36,977)
Net plant in service	32,684
Energy Equipment | Nuclear production
Property, Plant and Equipment and Finite-Lived Intangible Assets [Line Items]
Gross Plant	817,665
Accumulated Depreciation	(271,173)
Net plant in service	546,492
Energy Equipment | Steam and other
Property, Plant and Equipment and Finite-Lived Intangible Assets [Line Items]
Gross Plant	668,666
Accumulated Depreciation	(264,019)
Net plant in service	404,647
Energy Equipment | Total production
Property, Plant and Equipment and Finite-Lived Intangible Assets [Line Items]
Gross Plant	1,486,331
Accumulated Depreciation	(535,192)
Net plant in service	951,139
Energy Equipment | Transmission
Property, Plant and Equipment and Finite-Lived Intangible Assets [Line Items]
Gross Plant	432,674
Accumulated Depreciation	(246,175)
Net plant in service	186,499
Energy Equipment | Distribution
Property, Plant and Equipment and Finite-Lived Intangible Assets [Line Items]
Gross Plant	965,674
Accumulated Depreciation	(337,513)
Net plant in service	628,161
Energy Equipment | General
Property, Plant and Equipment and Finite-Lived Intangible Assets [Line Items]
Gross Plant	122,209
Accumulated Depreciation	(58,231)
Net plant in service	$ 63,978