Regulatory Matters (Details 3) (USD $)	Jun. 30, 2014	Dec. 31, 2013
Detail of regulatory assets
Regulatory assets, current	$ 78,000,000	$ 97,000,000
Regulatory assets, non-current	755,174,000	711,712,000
Pension and other postretirement benefits
Detail of regulatory assets
Regulatory assets, non-current	342,000,000	314,000,000
Income taxes - allowance for funds used during construction ("AFUDC") equity
Detail of regulatory assets
Regulatory assets, current	4,000,000	4,000,000
Regulatory assets, non-current	108,000,000	105,000,000
Deferred fuel and purchased power - mark-to-market
Detail of regulatory assets
Regulatory assets, current		5,000,000
Regulatory assets, non-current	17,000,000	29,000,000
Transmission vegetation management
Detail of regulatory assets
Regulatory assets, current	9,000,000	9,000,000
Regulatory assets, non-current	9,000,000	14,000,000
Coal reclamation
Detail of regulatory assets
Regulatory assets, current	8,000,000	8,000,000
Regulatory assets, non-current	14,000,000	18,000,000
Palo Verde VIE
Detail of regulatory assets
Regulatory assets, non-current	43,000,000	41,000,000
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	1,000,000	21,000,000
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	15,000,000
Loss on reacquired debt
Detail of regulatory assets
Regulatory assets, current	1,000,000	1,000,000
Regulatory assets, non-current	17,000,000	17,000,000
Income taxes - investment tax credit basis adjustment
Detail of regulatory assets
Regulatory assets, current	2,000,000	1,000,000
Regulatory assets, non-current	47,000,000	39,000,000
Pension and other postretirement benefits deferral
Detail of regulatory assets
Regulatory assets, current	8,000,000	8,000,000
Regulatory assets, non-current		4,000,000
Four Corners cost deferral
Detail of regulatory assets
Regulatory assets, non-current	55,000,000	37,000,000
Lost fixed cost recovery
Detail of regulatory assets
Regulatory assets, current	34,000,000	25,000,000
Transmission cost adjustor
Detail of regulatory assets
Regulatory assets, current	5,000,000	8,000,000
Regulatory assets, non-current		2,000,000
Retired power plant costs
Detail of regulatory assets
Regulatory assets, current	3,000,000	3,000,000
Regulatory assets, non-current	16,000,000	18,000,000
Deferred property taxes
Detail of regulatory assets
Regulatory assets, non-current	24,000,000	11,000,000
Other
Detail of regulatory assets
Regulatory assets, current	1,000,000	2,000,000
Regulatory assets, non-current	$ 12,000,000	$ 14,000,000