CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
CURRENT ASSETS
Cash and cash equivalents	$ 33,583	$ 110,188
Customer and other receivables	284,183	324,207
Accrued unbilled revenues	125,239	103,292
Allowance for doubtful accounts	(3,748)	(7,981)
Materials and supplies (at average cost)	204,387	181,414
Fossil fuel (at average cost)	22,000	21,575
Deferred income taxes (Note 4)	130,571	124,897
Income tax receivable (Note 4)	6,466	2,483
Assets from risk management activities (Note 18)	30,264	73,788
Deferred fuel and purchased power regulatory asset (Note 3)	27,549
Other regulatory assets (Note 3)	69,072	62,286
Other current assets	26,904	28,362
Total current assets	956,470	1,024,511
INVESTMENTS AND OTHER ASSETS
Assets from risk management activities (Note 18)	49,322	39,032
Nuclear decommissioning trust (Notes 14 and 23)	513,733	469,886
Other assets	64,588	116,216
Total investments and other assets	627,643	625,134
PROPERTY, PLANT AND EQUIPMENT (Notes 1, 6, 9 and 10)
Plant in service and held for future use	13,753,971	13,201,960
Accumulated depreciation and amortization	(4,709,991)	(4,514,204)
Net	9,043,980	8,687,756
Construction work in progress	496,745	459,361
Palo Verde sale leaseback, net of accumulated depreciation of $218,186 and $213,094 (Note 20)	132,864	137,956
Intangible assets, net of accumulated amortization of $373,706 and $330,584	170,571	184,952
Nuclear fuel, net of accumulated amortization of $113,375 and $85,270	118,098	108,794
Total property, plant and equipment	9,962,258	9,578,819
DEFERRED DEBITS
Regulatory assets (Notes 1, 3 and 4)	1,352,079	986,370
Income tax receivable (Note 4)	68,633	65,103
Other	143,935	113,061
Total deferred debits	1,564,647	1,164,534
TOTAL ASSETS	13,111,018	12,392,998
CURRENT LIABILITIES
Accounts payable	326,987	236,354
Accrued taxes	120,289	104,711
Accrued interest	54,872	54,831
Short-term borrowings (Note 5)		16,600
Current maturities of long-term debt (Note 6)	477,435	631,879
Customer deposits	72,176	68,322
Liabilities from risk management activities (Note 18)	53,968	58,976
Deferred fuel and purchased power regulatory liability (Note 3)		58,442
Other regulatory liabilities (Note 3)	88,362	80,526
Other current liabilities	148,616	139,063
Total current liabilities	1,342,705	1,449,704
LONG-TERM DEBT LESS CURRENT MATURITIES (Note 6)
Long-term debt less current maturities	2,953,507	2,948,991
Palo Verde sale leaseback lessor notes less current maturities (Note 20)	65,547	96,803
Total long-term debt less current maturities	3,019,054	3,045,794
DEFERRED CREDITS AND OTHER
Deferred income taxes (Note 4)	1,925,388	1,863,861
Regulatory liabilities (Notes 1 and 3)	737,332	614,063
Liability for asset retirements (Note 12)	279,643	328,571
Liabilities for pension and other postretirement benefits (Note 8)	1,268,910	813,121
Liabilities from risk management activities (Note 18)	82,495	65,390
Customer advances	116,805	121,645
Coal mine reclamation	117,896	117,243
Unrecognized tax benefits (Note 4)	72,270	66,349
Other	217,934	132,031
Total deferred credits and other	4,818,673	4,122,274
COMMITMENTS AND CONTINGENCIES (SEE NOTES)
EQUITY (Note 7)
Common stock, no par value; authorized 150,000,000 shares, issued 109,356,974 at end of 2011 and 108,820,067 at end of 2010	2,444,247	2,421,372
Treasury stock at cost; 111,161 shares at end of 2011 and 50,410 at end of 2010	(4,717)	(2,239)
Total common stock	2,439,530	2,419,133
Retained earnings	1,534,483	1,423,961
Accumulated other comprehensive loss:
Pension and other postretirement benefits (Note 8)	(65,447)	(59,420)
Derivative instruments	(86,716)	(100,347)
Total accumulated other comprehensive loss	(152,163)	(159,767)
Total shareholders' equity	3,821,850	3,683,327
Noncontrolling interests (Note 20)	108,736	91,899
Total equity	3,930,586	3,775,226
TOTAL LIABILITIES AND EQUITY	$ 13,111,018	$ 12,392,998