CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
CURRENT ASSETS
Cash and cash equivalents	$ 3,839	$ 13,892
Customer and other receivables	321,053	305,147
Accrued unbilled revenues	207,887	112,434
Allowance for doubtful accounts	(3,769)	(2,513)
Materials and supplies (at average cost)	263,370	264,012
Fossil fuel (at average cost)	47,591	25,258
Assets from risk management activities (Note 7)	3,316	1,931
Deferred fuel and purchased power regulatory asset (Note 4)	74,898	75,637
Other regulatory assets (Note 4)	154,661	172,451
Other current assets	45,865	48,039
Total current assets	1,118,711	1,016,288
INVESTMENTS AND OTHER ASSETS
Nuclear decommissioning trust (Note 12)	873,643	871,000
Other special use funds (Note 12)	216,338	32,542
Other assets	59,137	52,040
Total investments and other assets	1,149,118	955,582
PROPERTY, PLANT AND EQUIPMENT
Plant in service and held for future use	18,328,611	17,798,061
Accumulated depreciation and amortization	(6,245,809)	(6,128,535)
Net	12,082,802	11,669,526
Construction work in progress	1,140,611	1,291,498
Palo Verde sale leaseback, net of accumulated depreciation (Note 6)	107,710	109,645
Intangible assets, net of accumulated amortization	257,040	257,189
Nuclear fuel, net of accumulated amortization	119,256	117,408
Assets held for sale (Note 8)	95,364	0
Total property, plant and equipment	13,802,783	13,445,266
DEFERRED DEBITS
Regulatory assets (Note 4)	1,233,062	1,202,302
Assets for other postretirement benefits (Note 5)	47,619	268,978
Other	140,880	130,666
Total deferred debits	1,421,561	1,601,946
TOTAL ASSETS	17,492,173	17,019,082
CURRENT LIABILITIES
Accounts payable	260,285	256,442
Accrued taxes	156,362	148,946
Accrued interest	56,248	56,397
Common dividends payable	77,821	77,667
Short-term borrowings (Note 3)	616,249	95,400
Current maturities of long-term debt (Note 3)	600,000	82,000
Customer deposits	89,681	70,388
Liabilities from risk management activities (Note 7)	49,096	59,252
Liabilities for asset retirements	9,184	4,745
Regulatory liabilities (Note 4)	156,757	100,086
Other current liabilities	167,202	246,529
Total current liabilities	2,238,885	1,197,852
DEFERRED CREDITS AND OTHER
Deferred income taxes	1,727,700	1,690,805
Regulatory liabilities (Note 4)	2,389,002	2,452,536
Liabilities for asset retirements	677,341	674,784
Liabilities for pension benefits (Note 5)	319,604	327,300
Liabilities from risk management activities (Note 7)	46,347	37,170
Customer advances	118,459	113,996
Coal mine reclamation	213,137	231,597
Deferred investment tax credit	202,797	205,575
Unrecognized tax benefits	13,416	13,115
Liabilities held for sale (Note 8)	26,457	0
Other	168,069	148,909
Total deferred credits and other	5,902,329	5,895,787
COMMITMENTS AND CONTINGENCIES (SEE NOTE 8)
EQUITY
Common stock, no par value; authorized 150,000,000 shares, 111,990,222 and 111,816,170 issued at respective dates	2,624,672	2,614,805
Treasury stock at cost; 17,633 and 64,463 shares at respective dates	(1,431)	(5,624)
Total common stock	2,623,241	2,609,181
Retained earnings	2,465,402	2,442,511
Accumulated other comprehensive loss	(56,624)	(45,002)
Total shareholders’ equity	5,032,019	5,006,690
Noncontrolling interests (Note 6)	127,415	129,040
Total equity	5,159,434	5,135,730
Long-term debt less current maturities (Note 3)	4,191,525	4,789,713
TOTAL LIABILITIES AND EQUITY	17,492,173	17,019,082
APS
CURRENT ASSETS
Cash and cash equivalents	3,760	13,851
Customer and other receivables	299,279	292,791
Accrued unbilled revenues	207,887	112,434
Allowance for doubtful accounts	(3,769)	(2,513)
Materials and supplies (at average cost)	263,370	262,630
Fossil fuel (at average cost)	47,591	25,258
Assets from risk management activities (Note 7)	3,316	1,931
Deferred fuel and purchased power regulatory asset (Note 4)	74,898	75,637
Other regulatory assets (Note 4)	154,661	172,451
Other current assets	42,463	41,055
Total current assets	1,093,456	995,525
INVESTMENTS AND OTHER ASSETS
Nuclear decommissioning trust (Note 12)	873,643	871,000
Other special use funds (Note 12)	216,338	30,358
Other assets	40,868	36,796
Total investments and other assets	1,130,849	938,154
PROPERTY, PLANT AND EQUIPMENT
Plant in service and held for future use	18,325,124	17,654,078
Accumulated depreciation and amortization	(6,242,574)	(6,041,965)
Net	12,082,550	11,612,113
Construction work in progress	1,140,611	1,266,636
Palo Verde sale leaseback, net of accumulated depreciation (Note 6)	107,710	109,645
Intangible assets, net of accumulated amortization	256,885	257,028
Nuclear fuel, net of accumulated amortization	119,256	117,408
Total property, plant and equipment	13,707,012	13,362,830
DEFERRED DEBITS
Regulatory assets (Note 4)	1,233,062	1,202,302
Assets for other postretirement benefits (Note 5)	43,911	265,139
Other	129,362	129,801
Total deferred debits	1,406,335	1,597,242
TOTAL ASSETS	17,337,652	16,893,751
CURRENT LIABILITIES
Accounts payable	253,191	247,852
Accrued taxes	183,761	157,349
Accrued interest	55,383	55,533
Common dividends payable	77,800	77,700
Short-term borrowings (Note 3)	499,949	0
Current maturities of long-term debt (Note 3)	600,000	82,000
Customer deposits	89,681	70,388
Liabilities from risk management activities (Note 7)	49,096	59,252
Liabilities for asset retirements	9,184	4,192
Regulatory liabilities (Note 4)	156,757	100,086
Other current liabilities	162,963	243,922
Total current liabilities	2,137,765	1,098,274
DEFERRED CREDITS AND OTHER
Deferred income taxes	1,755,897	1,742,485
Regulatory liabilities (Note 4)	2,389,002	2,452,536
Liabilities for asset retirements	677,341	666,527
Liabilities for pension benefits (Note 5)	299,747	306,542
Liabilities from risk management activities (Note 7)	46,347	37,170
Customer advances	118,459	113,996
Coal mine reclamation	213,137	215,830
Deferred investment tax credit	202,797	205,575
Unrecognized tax benefits	44,177	43,876
Other	147,011	133,779
Total deferred credits and other	5,893,915	5,918,316
COMMITMENTS AND CONTINGENCIES (SEE NOTE 8)
EQUITY
Total common stock	178,162	178,162
Additional paid-in capital	2,571,696	2,571,696
Retained earnings	2,570,816	2,533,954
Accumulated other comprehensive loss	(35,159)	(26,983)
Total shareholders’ equity	5,285,515	5,256,829
Noncontrolling interests (Note 6)	127,415	129,040
Total equity	5,412,930	5,385,869
Long-term debt less current maturities (Note 3)	3,893,042	4,491,292
Total capitalization	9,305,972	9,877,161
TOTAL LIABILITIES AND EQUITY	$ 17,337,652	$ 16,893,751