CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
CURRENT ASSETS
Cash and cash equivalents	$ 6,109	$ 5,766
Customer and other receivables	249,568	267,887
Accrued unbilled revenues	114,077	137,170
Allowance for doubtful accounts	(2,455)	(4,069)
Materials and supplies (at average cost)	280,857	269,065
Fossil fuel (at average cost)	26,294	25,029
Assets from risk management activities (Note 7)	763	1,113
Deferred fuel and purchased power regulatory asset (Note 4)	7,583	37,164
Other regulatory assets (Note 4)	127,642	129,738
Other current assets	65,951	56,128
Total current assets	876,389	924,991
INVESTMENTS AND OTHER ASSETS
Nuclear decommissioning trust (Notes 11 and 12)	919,309	851,134
Other special use funds (Notes 11 and 12)	238,207	236,101
Other assets	99,446	103,247
Total investments and other assets	1,256,962	1,190,482
PROPERTY, PLANT AND EQUIPMENT
Plant in service and held for future use	18,763,499	18,736,628
Accumulated depreciation and amortization	(6,398,512)	(6,366,014)
Net	12,364,987	12,370,614
Construction work in progress	1,233,018	1,170,062
Palo Verde sale leaseback, net of accumulated depreciation (Note 6)	104,808	105,775
Intangible assets, net of accumulated amortization	267,998	262,902
Nuclear fuel, net of accumulated amortization	142,610	120,217
Total property, plant and equipment	14,113,421	14,029,570
DEFERRED DEBITS
Regulatory assets (Note 4)	1,321,507	1,342,941
Operating lease right-of-use assets (Note 16)	193,897	0
Assets for other postretirement benefits (Note 5)	52,674	46,906
Other	39,257	129,312
Total deferred debits	1,607,335	1,519,159
TOTAL ASSETS	17,854,107	17,664,202
CURRENT LIABILITIES
Accounts payable	263,656	277,336
Accrued taxes	199,949	154,819
Accrued interest	50,074	61,107
Common dividends payable	0	82,675
Short-term borrowings (Note 3)	244,050	76,400
Current maturities of long-term debt (Note 3)	250,000	500,000
Customer deposits	87,263	91,174
Liabilities from risk management activities (Note 7)	33,289	35,506
Liabilities for asset retirements	22,823	19,842
Operating lease liabilities (Note 16)	65,435	0
Regulatory liabilities (Note 4)	260,404	165,876
Other current liabilities	114,361	184,229
Total current liabilities	1,591,304	1,648,964
DEFERRED CREDITS AND OTHER
Deferred income taxes	1,811,689	1,807,421
Regulatory liabilities (Note 4)	2,272,082	2,325,976
Liabilities for asset retirements	712,885	706,703
Liabilities for pension benefits (Note 5)	384,492	443,170
Liabilities from risk management activities (Note 7)	14,844	24,531
Customer advances	155,894	137,153
Coal mine reclamation	214,037	212,785
Deferred investment tax credit	200,052	200,405
Unrecognized tax benefits	26,042	22,517
Operating lease liabilities (Note 16)	53,704	0
Other	149,249	147,640
Total deferred credits and other	5,994,970	6,028,301
COMMITMENTS AND CONTINGENCIES (SEE NOTE 8)
EQUITY
Common stock, no par value; authorized 150,000,000 shares, 112,340,322 and 112,159,896 issued at respective dates	2,644,063	2,634,265
Treasury stock at cost; 63,271 and 58,135 shares at respective dates	(5,586)	(4,825)
Total common stock	2,638,477	2,629,440
Retained earnings	2,659,086	2,641,183
Accumulated other comprehensive loss	(46,501)	(47,708)
Total shareholders’ equity	5,251,062	5,222,915
Noncontrolling interests (Note 6)	130,663	125,790
Total equity	5,381,725	5,348,705
Long-term debt less current maturities (Note 3)	4,886,108	4,638,232
TOTAL LIABILITIES AND EQUITY	17,854,107	17,664,202
APS
CURRENT ASSETS
Cash and cash equivalents	6,080	5,707
Customer and other receivables	238,270	257,654
Accrued unbilled revenues	114,077	137,170
Allowance for doubtful accounts	(2,455)	(4,069)
Materials and supplies (at average cost)	280,857	269,065
Fossil fuel (at average cost)	26,294	25,029
Assets from risk management activities (Note 7)	763	1,113
Deferred fuel and purchased power regulatory asset (Note 4)	7,583	37,164
Other regulatory assets (Note 4)	127,642	129,738
Other current assets	44,417	35,111
Total current assets	843,528	893,682
INVESTMENTS AND OTHER ASSETS
Nuclear decommissioning trust (Notes 11 and 12)	919,309	851,134
Other special use funds (Notes 11 and 12)	238,207	236,101
Other assets	42,090	40,817
Total investments and other assets	1,199,606	1,128,052
PROPERTY, PLANT AND EQUIPMENT
Plant in service and held for future use	18,760,012	18,733,142
Accumulated depreciation and amortization	(6,395,265)	(6,362,771)
Net	12,364,747	12,370,371
Construction work in progress	1,233,018	1,170,062
Palo Verde sale leaseback, net of accumulated depreciation (Note 6)	104,808	105,775
Intangible assets, net of accumulated amortization	267,842	262,746
Nuclear fuel, net of accumulated amortization	142,610	120,217
Total property, plant and equipment	14,113,025	14,029,171
DEFERRED DEBITS
Regulatory assets (Note 4)	1,321,507	1,342,941
Operating lease right-of-use assets (Note 16)	191,957	0
Assets for other postretirement benefits (Note 5)	48,961	43,212
Other	38,299	128,265
Total deferred debits	1,600,724	1,514,418
TOTAL ASSETS	17,756,883	17,565,323
CURRENT LIABILITIES
Accounts payable	257,124	266,277
Accrued taxes	230,591	176,357
Accrued interest	47,585	60,228
Common dividends payable	0	82,700
Short-term borrowings (Note 3)	157,500	0
Current maturities of long-term debt (Note 3)	250,000	500,000
Customer deposits	87,263	91,174
Liabilities from risk management activities (Note 7)	33,289	35,506
Liabilities for asset retirements	22,823	19,842
Operating lease liabilities (Note 16)	65,267	0
Regulatory liabilities (Note 4)	260,404	165,876
Other current liabilities	114,665	178,137
Total current liabilities	1,526,511	1,576,097
DEFERRED CREDITS AND OTHER
Deferred income taxes	1,815,368	1,812,664
Regulatory liabilities (Note 4)	2,272,082	2,325,976
Liabilities for asset retirements	712,885	706,703
Liabilities for pension benefits (Note 5)	367,296	425,404
Liabilities from risk management activities (Note 7)	14,844	24,531
Customer advances	155,894	137,153
Coal mine reclamation	214,037	212,785
Deferred investment tax credit	200,052	200,405
Unrecognized tax benefits	42,084	41,861
Operating lease liabilities (Note 16)	51,805	0
Other	125,844	125,511
Total deferred credits and other	5,972,191	6,012,993
COMMITMENTS AND CONTINGENCIES (SEE NOTE 8)
EQUITY
Total common stock	178,162	178,162
Additional paid-in capital	2,721,696	2,721,696
Retained earnings	2,816,532	2,788,256
Accumulated other comprehensive loss	(26,027)	(27,107)
Total shareholders’ equity	5,690,363	5,661,007
Noncontrolling interests (Note 6)	130,663	125,790
Total equity	5,821,026	5,786,797
Long-term debt less current maturities (Note 3)	4,437,155	4,189,436
Total capitalization	10,258,181	9,976,233
TOTAL LIABILITIES AND EQUITY	$ 17,756,883	$ 17,565,323