Regulatory Matters (Details 2) (USD $)	Sep. 30, 2012	Dec. 31, 2011
Detail of regulatory assets
Regulatory assets, current	$ 122,000,000	$ 97,000,000
Regulatory assets, non-current	1,250,792,000	1,352,079,000
Pension and other postretirement benefits
Detail of regulatory assets
Regulatory assets, non-current	939,000,000	1,023,000,000
Income taxes allowance for funds used during construction (AFUDC) equity
Detail of regulatory assets
Regulatory assets, current	3,000,000	3,000,000
Regulatory assets, non-current	91,000,000	81,000,000
Deferred fuel and purchased power - mark-to-market
Detail of regulatory assets
Regulatory assets, current	11,000,000	43,000,000
Regulatory assets, non-current	16,000,000	34,000,000
Transmission vegetation management
Detail of regulatory assets
Regulatory assets, current	9,000,000	9,000,000
Regulatory assets, non-current	25,000,000	32,000,000
Coal reclamation
Detail of regulatory assets
Regulatory assets, current	8,000,000	2,000,000
Regulatory assets, non-current	26,000,000	35,000,000
Palo Verde VIE
Detail of regulatory assets
Regulatory assets, non-current	37,000,000	35,000,000
Deferred compensation
Detail of regulatory assets
Regulatory assets, non-current	35,000,000	33,000,000
Deferred fuel and purchased power
Detail of regulatory assets
Regulatory assets, current	68,000,000	28,000,000
Tax expense of Medicare subsidy
Detail of regulatory assets
Regulatory assets, current	2,000,000	2,000,000
Regulatory assets, non-current	17,000,000	18,000,000
Loss on reacquired debt
Detail of regulatory assets
Regulatory assets, current	1,000,000	1,000,000
Regulatory assets, non-current	18,000,000	19,000,000
Income taxes - investment tax credit basis adjustment
Detail of regulatory assets
Regulatory assets, current	1,000,000
Regulatory assets, non-current	17,000,000	15,000,000
Pension and other postretirement benefits deferral
Detail of regulatory assets
Regulatory assets, current	8,000,000
Regulatory assets, non-current	15,000,000	12,000,000
Demand side management
Detail of regulatory assets
Regulatory assets, current		7,000,000
Regulatory assets, non-current		1,000,000
Other.
Detail of regulatory assets
Regulatory assets, current	11,000,000	2,000,000
Regulatory assets, non-current	$ 15,000,000	$ 14,000,000