Regulatory Matters (Details 2) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Detail of regulatory assets
Regulatory assets, current	$ 120,000,000	$ 144,000,000
Regulatory assets, non-current	1,105,882,000	1,099,900,000
Pension and other postretirement benefits
Detail of regulatory assets
Regulatory assets, non-current	754,000,000	780,000,000
Income taxes - allowance for equity funds used during construction
Detail of regulatory assets
Regulatory assets, current	4,000,000	4,000,000
Regulatory assets, non-current	105,000,000	92,000,000
Deferred fuel and purchased power - mark-to-market
Detail of regulatory assets
Regulatory assets, current	15,000,000	19,000,000
Regulatory assets, non-current	24,000,000	21,000,000
Transmission vegetation management
Detail of regulatory assets
Regulatory assets, current	9,000,000	9,000,000
Regulatory assets, non-current	16,000,000	23,000,000
Coal reclamation
Detail of regulatory assets
Regulatory assets, current	8,000,000	8,000,000
Regulatory assets, non-current	20,000,000	24,000,000
Palo Verde VIE
Detail of regulatory assets
Regulatory assets, non-current	40,000,000	38,000,000
Deferred compensation
Detail of regulatory assets
Regulatory assets, non-current	36,000,000	34,000,000
Deferred fuel and purchased power
Detail of regulatory assets
Regulatory assets, current	37,000,000	73,000,000
Retired power plant costs
Detail of regulatory assets
Regulatory assets, current	3,000,000
Regulatory assets, non-current	19,000,000
Tax expense of Medicare subsidy
Detail of regulatory assets
Regulatory assets, current	2,000,000	2,000,000
Regulatory assets, non-current	15,000,000	17,000,000
Loss on reacquired debt
Detail of regulatory assets
Regulatory assets, current	1,000,000	2,000,000
Regulatory assets, non-current	17,000,000	18,000,000
Income taxes - investment tax credit basis adjustment
Detail of regulatory assets
Regulatory assets, current	1,000,000	1,000,000
Regulatory assets, non-current	30,000,000	26,000,000
Pension and other postretirement benefits deferral
Detail of regulatory assets
Regulatory assets, current	8,000,000	8,000,000
Regulatory assets, non-current	6,000,000	13,000,000
Lost fixed cost recovery
Detail of regulatory assets
Regulatory assets, current	19,000,000	7,000,000
Transmission cost adjustor
Detail of regulatory assets
Regulatory assets, current	12,000,000	10,000,000
Regulatory assets, non-current	2,000,000
Other
Detail of regulatory assets
Regulatory assets, current	1,000,000	1,000,000
Regulatory assets, non-current	$ 22,000,000	$ 14,000,000