CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
CURRENT ASSETS
Cash and cash equivalents	$ 26,202	$ 33,583
Customer and other receivables	277,225	284,183
Accrued unbilled revenues	94,845	125,239
Allowance for doubtful accounts	(3,340)	(3,748)
Materials and supplies (at average cost)	218,096	204,387
Fossil fuel (at average cost)	31,334	22,000
Deferred income taxes (Note 4)	152,191	130,571
Income tax receivable (Note 4)	2,423	6,466
Assets from risk management activities (Note 18)	25,699	30,264
Deferred fuel and purchased power regulatory asset (Note 3)	72,692	27,549
Other regulatory assets (Note 3)	71,257	69,072
Other current assets	37,102	26,904
Total current assets	1,005,726	956,470
INVESTMENTS AND OTHER ASSETS
Assets from risk management activities (Note 18)	35,891	49,322
Nuclear decommissioning trust (Notes 14 and 22)	570,625	513,733
Other assets	62,694	64,588
Total investments and other assets	669,210	627,643
PROPERTY, PLANT AND EQUIPMENT (Notes 1, 6 and 10)
Plant in service and held for future use	14,346,367	13,753,971
Accumulated depreciation and amortization	(4,929,613)	(4,709,991)
Net	9,416,754	9,043,980
Construction work in progress	565,716	496,745
Palo Verde sale leaseback, net of accumulated depreciation of $222,055 and $218,186 (Note 20)	128,995	132,864
Intangible assets, net of accumulated amortization of $411,543 and $373,706	162,150	170,571
Nuclear fuel, net of accumulated amortization of $133,950 and $113,375	122,778	118,098
Total property, plant and equipment	10,396,393	9,962,258
DEFERRED DEBITS
Regulatory assets (Notes 1, 3 and 4)	1,099,900	1,352,079
Income tax receivable (Note 4)	70,389	68,633
Other	137,997	143,935
Total deferred debits	1,308,286	1,564,647
TOTAL ASSETS	13,379,615	13,111,018
CURRENT LIABILITIES
Accounts payable	221,312	326,987
Accrued taxes (Note 4)	124,939	120,289
Accrued interest	49,380	54,872
Common dividends payable	59,789
Short-term borrowings (Note 5)	92,175
Current maturities of long-term debt (Note 6)	122,828	477,435
Customer deposits	79,689	72,176
Liabilities from risk management activities (Note 18)	73,741	53,968
Regulatory liabilities (Note 3)	88,116	88,362
Other current liabilities	171,573	148,616
Total current liabilities	1,083,542	1,342,705
LONG-TERM DEBT LESS CURRENT MATURITIES (Note 6)
Long-term debt less current maturities	3,160,219	2,953,507
Palo Verde sale leaseback lessor notes less current maturities (Note 20)	38,869	65,547
Total long-term debt less current maturities	3,199,088	3,019,054
DEFERRED CREDITS AND OTHER
Deferred income taxes (Note 4)	2,151,371	1,925,388
Regulatory liabilities (Notes 1, 3 and 4)	759,201	737,332
Liability for asset retirements (Note 12)	357,097	279,643
Liabilities for pension and other postretirement benefits (Note 8)	1,058,755	1,268,910
Liabilities from risk management activities (Note 18)	85,264	82,495
Customer advances	109,359	116,805
Coal mine reclamation	118,860	117,896
Unrecognized tax benefits (Note 4)	71,135	72,270
Other	283,654	217,934
Total deferred credits and other	4,994,696	4,818,673
COMMITMENTS AND CONTINGENCIES (SEE NOTES)
EQUITY (Note 7)
Common stock, no par value; authorized 150,000,000 shares, issued 109,837,957 at end of 2012 and 109,356,974 at end of 2011	2,466,923	2,444,247
Treasury stock at cost; 95,192 shares at end of 2012 and 111,161 at end of 2011	(4,211)	(4,717)
Total common stock	2,462,712	2,439,530
Retained earnings	1,624,102	1,534,483
Accumulated other comprehensive loss:
Pension and other postretirement benefits (Note 8)	(64,416)	(65,447)
Derivative instruments (Note 18)	(49,592)	(86,716)
Total accumulated other comprehensive loss	(114,008)	(152,163)
Total shareholders' equity	3,972,806	3,821,850
Noncontrolling interests (Note 20)	129,483	108,736
Total equity	4,102,289	3,930,586
TOTAL LIABILITIES AND EQUITY	$ 13,379,615	$ 13,111,018