CONDENSED CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
CURRENT ASSETS
Cash and cash equivalents	$ 25,109	$ 26,202
Customer and other receivables	267,937	277,225
Accrued unbilled revenues	90,147	94,845
Allowance for doubtful accounts	(2,537)	(3,340)
Materials and supplies (at average cost)	223,605	218,096
Fossil fuel (at average cost)	35,211	31,334
Deferred income taxes	75,866	152,191
Income tax receivable (Note 5)	2,856	2,423
Assets from risk management activities (Note 7)	20,346	25,699
Deferred fuel and purchased power regulatory asset (Note 3)	41,315	72,692
Other regulatory assets (Note 3)	52,872	71,257
Other current assets	39,050	37,102
Total current assets	871,777	1,005,726
INVESTMENTS AND OTHER ASSETS
Assets from risk management activities (Note 7)	34,047	35,891
Nuclear decommissioning trust (Note 13)	596,168	570,625
Other assets	64,325	62,694
Total investments and other assets	694,540	669,210
PROPERTY, PLANT AND EQUIPMENT
Plant in service and held for future use	14,494,326	14,346,367
Accumulated depreciation and amortization	(4,997,126)	(4,929,613)
Net	9,497,200	9,416,754
Construction work in progress	498,124	565,716
Palo Verde sale leaseback, net of accumulated depreciation (Note 6)	128,027	128,995
Intangible assets, net of accumulated amortization	162,978	162,150
Nuclear fuel, net of accumulated amortization	140,909	122,778
Total property, plant and equipment	10,427,238	10,396,393
DEFERRED DEBITS
Regulatory assets (Note 3)	1,097,389	1,099,900
Income tax receivable (Note 5)	70,828	70,389
Other	139,155	137,997
Total deferred debits	1,307,372	1,308,286
TOTAL ASSETS	13,300,927	13,379,615
CURRENT LIABILITIES
Accounts payable	212,078	221,312
Accrued taxes (Note 5)	164,554	124,939
Accrued interest	44,818	49,380
Common dividends payable		59,789
Short-term borrowings		92,175
Current maturities of long-term debt	122,828	122,828
Customer deposits	80,783	79,689
Liabilities from risk management activities (Note 7)	65,354	73,741
Regulatory liabilities (Note 3)	76,640	88,116
Other current liabilities	124,456	171,573
Total current liabilities	891,511	1,083,542
LONG-TERM DEBT LESS CURRENT MATURITIES
Long-term debt less current maturities	3,265,589	3,160,219
Palo Verde sale leaseback lessor notes less current maturities (Note 6)	38,869	38,869
Total long-term debt less current maturities	3,304,458	3,199,088
DEFERRED CREDITS AND OTHER
Deferred income taxes	2,064,476	2,151,371
Regulatory liabilities (Note 3)	805,230	759,201
Liability for asset retirements	358,184	357,097
Liabilities for pension and other postretirement benefits (Note 4)	1,034,327	1,058,755
Liabilities from risk management activities (Note 7)	82,876	85,264
Customer advances	108,986	109,359
Coal mine reclamation	119,044	118,860
Unrecognized tax benefits (Note 5)	72,252	71,135
Other	307,253	283,654
Total deferred credits and other	4,952,628	4,994,696
COMMITMENTS AND CONTINGENCIES (SEE NOTES)
EQUITY (Note 8)
Common stock, no par value	2,484,347	2,466,923
Treasury stock	(10,482)	(4,211)
Total common stock	2,473,865	2,462,712
Retained earnings	1,648,521	1,624,102
Accumulated other comprehensive loss:
Pension and other postretirement benefits	(63,450)	(64,416)
Derivative instruments	(44,481)	(49,592)
Total accumulated other comprehensive loss	(107,931)	(114,008)
Total shareholders' equity	4,014,455	3,972,806
Noncontrolling interests (Note 6)	137,875	129,483
Total equity	4,152,330	4,102,289
TOTAL LIABILITIES AND EQUITY	$ 13,300,927	$ 13,379,615