CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
CURRENT ASSETS
Cash and cash equivalents	$ 25,688	$ 59,968
Customer and other receivables	430,150	313,576
Accrued unbilled revenues	190,531	132,197
Allowance for doubtful accounts (Note 2)	(25,303)	(19,782)
Materials and supplies (at average cost)	351,148	314,745
Income tax receivable	0	6,792
Fossil fuel (at average cost)	29,893	19,552
Assets from risk management activities (Note 7)	126,595	2,931
Deferred fuel and purchased power regulatory asset (Note 4)	375,181	175,835
Other regulatory assets (Note 4)	122,719	115,878
Other current assets	82,546	76,627
Total current assets	1,709,148	1,198,319
INVESTMENTS AND OTHER ASSETS
Nuclear decommissioning trusts (Notes 11 and 12)	1,225,485	1,138,435
Other special use funds (Notes 11 and 12)	374,843	254,509
Other assets	160,185	92,922
Total investments and other assets	1,760,513	1,485,866
PROPERTY, PLANT AND EQUIPMENT
Plant in service and held for future use	21,391,019	20,837,885
Accumulated depreciation and amortization	(7,368,125)	(7,110,310)
Net	14,022,894	13,727,575
Construction work in progress	1,162,844	937,384
Palo Verde sale leaseback, net of accumulated depreciation (Note 6)	95,133	98,036
Intangible assets, net of accumulated amortization	273,243	282,570
Nuclear fuel, net of accumulated amortization	119,487	113,645
Total property, plant and equipment	15,673,601	15,159,210
DEFERRED DEBITS
Regulatory assets (Note 4)	1,177,698	1,133,987
Operating lease right-of-use assets (Note 15)	649,381	505,064
Assets for pension and other postretirement benefits (Note 5)	529,715	502,992
Other	36,368	34,983
Total deferred debits	2,393,162	2,177,026
TOTAL ASSETS	21,536,424	20,020,421
CURRENT LIABILITIES
Accounts payable	353,591	318,585
Accrued taxes	253,504	159,551
Accrued interest	60,046	56,962
Common dividends payable	0	93,531
Short-term borrowings (Note 3)	125,000	169,000
Current maturities of long-term debt (Note 3)	150,000	0
Customer deposits	44,089	48,340
Liabilities from risk management activities (Note 7)	1,652	7,557
Liabilities for asset retirements (Note 16)	6,066	15,586
Operating lease liabilities (Note 15)	130,078	74,785
Regulatory liabilities (Note 4)	379,193	229,088
Other current liabilities	146,038	187,448
Total current liabilities	1,649,257	1,360,433
LONG-TERM DEBT LESS CURRENT MATURITIES (Note 3)	6,763,146	6,314,266
DEFERRED CREDITS AND OTHER
Deferred income taxes	2,289,366	2,135,403
Regulatory liabilities (Note 4)	2,431,212	2,450,169
Liabilities for asset retirements (Note 16)	752,011	689,497
Liabilities for pension benefits (Note 5)	160,972	166,484
Liabilities from risk management activities (Note 7)	0	11,062
Customer advances	247,334	221,032
Coal mine reclamation	173,486	170,097
Deferred investment tax credit	183,038	191,372
Unrecognized tax benefits	5,683	5,834
Operating lease liabilities (Note 15)	478,847	361,336
Other	215,608	190,643
Total deferred credits and other	6,937,557	6,592,929
COMMITMENTS AND CONTINGENCIES (NOTE 8)
EQUITY
Common stock, no par value; authorized 150,000,000 shares, 112,852,121 and 112,760,051 issued at respective dates	2,698,552	2,677,482
Treasury stock at cost; 36,153 and 72,006 shares at respective dates	(3,079)	(6,289)
Total common stock	2,695,473	2,671,193
Retained earnings	3,429,076	3,025,106
Accumulated other comprehensive loss	(59,666)	(62,796)
Total shareholders’ equity	6,064,883	5,633,503
Noncontrolling interests (Note 6)	121,581	119,290
Total equity	6,186,464	5,752,793
TOTAL LIABILITIES AND EQUITY	21,536,424	20,020,421
APS
CURRENT ASSETS
Cash and cash equivalents	19,298	57,310
Customer and other receivables	429,854	312,644
Accrued unbilled revenues	190,531	132,197
Allowance for doubtful accounts (Note 2)	(25,303)	(19,782)
Materials and supplies (at average cost)	351,148	314,745
Fossil fuel (at average cost)	29,893	19,552
Assets from risk management activities (Note 7)	126,595	2,931
Deferred fuel and purchased power regulatory asset (Note 4)	375,181	175,835
Other regulatory assets (Note 4)	122,719	115,878
Other current assets	55,061	47,593
Total current assets	1,674,977	1,158,903
INVESTMENTS AND OTHER ASSETS
Nuclear decommissioning trusts (Notes 11 and 12)	1,225,485	1,138,435
Other special use funds (Notes 11 and 12)	374,843	254,509
Other assets	109,526	46,010
Total investments and other assets	1,709,854	1,438,954
PROPERTY, PLANT AND EQUIPMENT
Plant in service and held for future use	21,387,558	20,834,424
Accumulated depreciation and amortization	(7,364,844)	(7,107,058)
Net	14,022,714	13,727,366
Construction work in progress	1,162,844	937,384
Palo Verde sale leaseback, net of accumulated depreciation (Note 6)	95,133	98,036
Intangible assets, net of accumulated amortization	273,088	282,415
Nuclear fuel, net of accumulated amortization	119,487	113,645
Total property, plant and equipment	15,673,266	15,158,846
DEFERRED DEBITS
Regulatory assets (Note 4)	1,177,698	1,133,987
Operating lease right-of-use assets (Note 15)	647,871	503,475
Assets for pension and other postretirement benefits (Note 5)	521,268	495,673
Other	35,560	34,413
Total deferred debits	2,382,397	2,167,548
TOTAL ASSETS	21,440,494	19,924,251
CURRENT LIABILITIES
Accounts payable	347,476	311,699
Accrued taxes	270,887	148,970
Accrued interest	57,707	56,322
Common dividends payable	0	93,500
Short-term borrowings (Note 3)	125,000	0
Customer deposits	44,089	48,340
Liabilities from risk management activities (Note 7)	1,652	7,557
Liabilities for asset retirements (Note 16)	6,066	15,586
Operating lease liabilities (Note 15)	129,980	74,695
Regulatory liabilities (Note 4)	379,193	229,088
Other current liabilities	141,822	190,420
Total current liabilities	1,503,872	1,176,177
LONG-TERM DEBT LESS CURRENT MATURITIES (Note 3)	6,266,212	5,817,945
DEFERRED CREDITS AND OTHER
Deferred income taxes	2,273,627	2,143,673
Regulatory liabilities (Note 4)	2,431,212	2,450,169
Liabilities for asset retirements (Note 16)	752,011	689,497
Liabilities for pension benefits (Note 5)	145,040	148,943
Liabilities from risk management activities (Note 7)	0	11,062
Customer advances	247,334	221,032
Coal mine reclamation	173,486	170,097
Deferred investment tax credit	183,038	191,372
Unrecognized tax benefits	40,052	39,410
Operating lease liabilities (Note 15)	477,244	359,653
Other	186,107	160,036
Total deferred credits and other	6,909,151	6,584,944
COMMITMENTS AND CONTINGENCIES (NOTE 8)
EQUITY
Common stock	178,162	178,162
Additional paid-in capital	2,871,696	2,871,696
Retained earnings	3,628,652	3,216,955
Accumulated other comprehensive loss	(38,832)	(40,918)
Total shareholders’ equity	6,639,678	6,225,895
Noncontrolling interests (Note 6)	121,581	119,290
Total equity	6,761,259	6,345,185
Total capitalization	13,027,471	12,163,130
TOTAL LIABILITIES AND EQUITY	$ 21,440,494	$ 19,924,251