Regulatory Matters (Details 2) (USD $)	Mar. 31, 2012	Dec. 31, 2011
Detail of regulatory assets
Regulatory assets, current	$ 87,000,000	$ 97,000,000
Regulatory assets, non-current	1,344,523,000	1,352,079,000
Pension and other postretirement benefits
Detail of regulatory assets
Regulatory assets, non-current	1,007,000,000	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	81,000,000	81,000,000
Deferred fuel and purchased power - mark-to-market
Detail of regulatory assets
Regulatory assets, current	58,000,000	43,000,000
Regulatory assets, non-current	34,000,000	34,000,000
Transmission vegetation management
Detail of regulatory assets
Regulatory assets, current	9,000,000	9,000,000
Regulatory assets, non-current	30,000,000	32,000,000
Coal reclamation
Detail of regulatory assets
Regulatory assets, current	2,000,000	2,000,000
Regulatory assets, non-current	34,000,000	35,000,000
Palo Verde VIE
Detail of regulatory assets
Regulatory assets, non-current	36,000,000	35,000,000
Deferred compensation
Detail of regulatory assets
Regulatory assets, non-current	34,000,000	33,000,000
Deferred fuel and purchased power
Detail of regulatory assets
Regulatory assets, current	5,000,000	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	19,000,000	18,000,000
Loss on reacquired debt
Detail of regulatory assets
Regulatory assets, current	1,000,000	1,000,000
Regulatory assets, non-current	19,000,000	19,000,000
Pension and other postretirement benefits deferral
Detail of regulatory assets
Regulatory assets, non-current	21,000,000	12,000,000
Demand side management
Detail of regulatory assets
Regulatory assets, current	5,000,000	7,000,000
Regulatory assets, non-current		1,000,000
Other.
Detail of regulatory assets
Regulatory assets, current	2,000,000	2,000,000
Regulatory assets, non-current	15,000,000	14,000,000
Income taxes - investment tax credit basis adjustment
Detail of regulatory assets
Regulatory assets, non-current	$ 15,000,000	$ 15,000,000