CONDENSED CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
CURRENT ASSETS
Cash and cash equivalents	$ 135,457	$ 26,202
Customer and other receivables	427,370	277,225
Accrued unbilled revenues	132,555	94,845
Allowance for doubtful accounts	(3,768)	(3,340)
Materials and supplies (at average cost)	223,385	218,096
Fossil fuel (at average cost)	34,959	31,334
Deferred income taxes	87,490	152,191
Income tax receivable (Note 5)	133,551	2,423
Assets from risk management activities (Note 7)	22,741	25,699
Deferred fuel and purchased power regulatory asset (Note 3)	37,383	72,692
Other regulatory assets (Note 3)	82,558	71,257
Other current assets	36,805	37,102
Total current assets	1,350,486	1,005,726
INVESTMENTS AND OTHER ASSETS
Assets from risk management activities (Note 7)	26,046	35,891
Nuclear decommissioning trust (Note 13)	612,640	570,625
Other assets	60,219	62,694
Total investments and other assets	698,905	669,210
PROPERTY, PLANT AND EQUIPMENT
Plant in service and held for future use	14,597,995	14,346,367
Accumulated depreciation and amortization	(5,101,498)	(4,929,613)
Net	9,496,497	9,416,754
Construction work in progress	605,987	565,716
Palo Verde sale leaseback, net of accumulated depreciation (Note 6)	126,092	128,995
Intangible assets, net of accumulated amortization	160,134	162,150
Nuclear fuel, net of accumulated amortization	140,356	122,778
Total property, plant and equipment	10,529,066	10,396,393
DEFERRED DEBITS
Regulatory assets (Note 3)	1,105,882	1,099,900
Income tax receivable (Note 5)		70,389
Other	138,332	137,997
Total deferred debits	1,244,214	1,308,286
TOTAL ASSETS	13,822,671	13,379,615
CURRENT LIABILITIES
Accounts payable	250,023	221,312
Accrued taxes (Note 5)	183,858	124,939
Accrued interest	45,811	49,380
Common dividends payable		59,789
Short-term borrowings		92,175
Current maturities of long-term debt (Note 2)	566,481	122,828
Customer deposits	77,254	79,689
Liabilities from risk management activities (Note 7)	53,468	73,741
Regulatory liabilities (Note 3)	88,409	88,116
Other current liabilities	181,639	171,573
Total current liabilities	1,446,943	1,083,542
LONG-TERM DEBT LESS CURRENT MATURITIES (Note 2)
Long-term debt less current maturities	2,782,901	3,160,219
Palo Verde sale leaseback lessor notes less current maturities (Note 6)	37,414	38,869
Total long-term debt less current maturities	2,820,315	3,199,088
DEFERRED CREDITS AND OTHER
Deferred income taxes	2,363,783	2,151,371
Regulatory liabilities (Note 3)	798,226	759,201
Liability for asset retirements	364,635	357,097
Liabilities for pension and other postretirement benefits (Note 4)	939,414	1,058,755
Deferred investment tax credit	115,984	99,819
Liabilities from risk management activities (Note 7)	67,662	85,264
Customer advances	109,667	109,359
Coal mine reclamation	114,764	118,860
Unrecognized tax benefits (Note 5)	81,797	71,135
Other	178,053	183,835
Total deferred credits and other	5,133,985	4,994,696
COMMITMENTS AND CONTINGENCIES (SEE NOTES)
EQUITY (Note 8)
Common stock, no par value	2,489,180	2,466,923
Treasury stock	(10,079)	(4,211)
Total common stock	2,479,101	2,462,712
Retained earnings	1,886,038	1,624,102
Accumulated other comprehensive loss:
Pension and other postretirement benefits	(63,181)	(64,416)
Derivative instruments	(26,154)	(49,592)
Total accumulated other comprehensive loss	(89,335)	(114,008)
Total shareholders' equity	4,275,804	3,972,806
Noncontrolling interests (Note 6)	145,624	129,483
Total equity	4,421,428	4,102,289
TOTAL LIABILITIES AND EQUITY	$ 13,822,671	$ 13,379,615