CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
CURRENT ASSETS
Cash and cash equivalents	$ 17,202	$ 59,968
Customer and other receivables	263,126	313,576
Accrued unbilled revenues	122,034	132,197
Allowance for doubtful accounts	(20,405)	(19,782)
Materials and supplies (at average cost)	314,702	314,745
Fossil fuel (at average cost)	24,396	19,552
Income tax receivable	0	6,792
Assets from risk management activities (Note 7)	22,611	2,931
Deferred fuel and purchased power regulatory asset (Note 4)	228,609	175,835
Other regulatory assets (Note 4)	111,271	115,878
Other current assets	86,238	76,627
Total current assets	1,169,784	1,198,319
INVESTMENTS AND OTHER ASSETS
Nuclear decommissioning trust (Notes 11 and 12)	1,159,699	1,138,435
Other special use funds (Notes 11 and 12)	357,506	254,509
Other assets	88,487	92,922
Total investments and other assets	1,605,692	1,485,866
PROPERTY, PLANT AND EQUIPMENT
Plant in service and held for future use	20,948,591	20,837,885
Accumulated depreciation and amortization	(7,189,708)	(7,110,310)
Net	13,758,883	13,727,575
Construction work in progress	1,056,991	937,384
Palo Verde sale leaseback, net of accumulated depreciation (Note 6)	97,068	98,036
Intangible assets, net of accumulated amortization	278,226	282,570
Nuclear fuel, net of accumulated amortization	124,533	113,645
Total property, plant and equipment	15,315,701	15,159,210
DEFERRED DEBITS
Regulatory assets (Note 4)	1,135,857	1,133,987
Operating lease right-of-use assets	502,959	505,064
Assets for pension and other postretirement benefits (Note 5)	418,427	502,992
Other	36,238	34,983
Total deferred debits	2,093,481	2,177,026
TOTAL ASSETS	20,184,658	20,020,421
CURRENT LIABILITIES
Accounts payable	309,145	318,585
Accrued taxes	213,536	159,551
Accrued interest	58,709	56,962
Common dividends payable	0	93,531
Short-term borrowings (Note 3)	214,750	169,000
Customer deposits	45,170	48,340
Liabilities from risk management activities (Note 7)	3,067	7,557
Liabilities for asset retirements	16,021	15,586
Operating lease liabilities	74,328	74,785
Regulatory liabilities (Note 4)	250,228	229,088
Other current liabilities	145,589	187,448
Total current liabilities	1,330,543	1,360,433
Long-term debt less current maturities (Note 3)	6,465,045	6,314,266
DEFERRED CREDITS AND OTHER
Deferred income taxes	2,134,471	2,135,403
Regulatory liabilities (Note 4)	2,427,769	2,450,169
Liabilities for asset retirements	693,383	689,497
Liabilities for pension benefits (Note 5)	164,230	166,484
Liabilities from risk management activities (Note 7)	6,928	11,062
Customer advances	220,999	221,032
Coal mine reclamation	171,227	170,097
Deferred investment tax credit	190,842	191,372
Unrecognized tax benefits	5,870	5,834
Operating lease liabilities	360,497	361,336
Other	206,174	190,643
Total deferred credits and other	6,582,390	6,592,929
COMMITMENTS AND CONTINGENCIES (NOTE 8)
EQUITY
Common stock, no par value; authorized 150,000,000 shares, 112,791,565 and 112,760,051 issued at respective dates	2,687,052	2,677,482
Treasury stock at cost; 44,338 and 72,006 shares at respective dates	(3,776)	(6,289)
Total common stock	2,683,276	2,671,193
Retained earnings	3,060,752	3,025,106
Accumulated other comprehensive loss	(61,512)	(62,796)
Total shareholders’ equity	5,682,516	5,633,503
Noncontrolling interests (Note 6)	124,164	119,290
Total equity	5,806,680	5,752,793
TOTAL LIABILITIES AND EQUITY	20,184,658	20,020,421
APS
CURRENT ASSETS
Cash and cash equivalents	14,536	57,310
Customer and other receivables	262,636	312,644
Accrued unbilled revenues	122,034	132,197
Allowance for doubtful accounts	(20,405)	(19,782)
Materials and supplies (at average cost)	314,702	314,745
Fossil fuel (at average cost)	24,396	19,552
Assets from risk management activities (Note 7)	22,611	2,931
Deferred fuel and purchased power regulatory asset (Note 4)	228,609	175,835
Other regulatory assets (Note 4)	111,271	115,878
Other current assets	56,987	47,593
Total current assets	1,137,377	1,158,903
INVESTMENTS AND OTHER ASSETS
Nuclear decommissioning trust (Notes 11 and 12)	1,159,699	1,138,435
Other special use funds (Notes 11 and 12)	357,506	254,509
Other assets	44,829	46,010
Total investments and other assets	1,562,034	1,438,954
PROPERTY, PLANT AND EQUIPMENT
Plant in service and held for future use	20,945,129	20,834,424
Accumulated depreciation and amortization	(7,186,452)	(7,107,058)
Net	13,758,677	13,727,366
Construction work in progress	1,056,991	937,384
Palo Verde sale leaseback, net of accumulated depreciation (Note 6)	97,068	98,036
Intangible assets, net of accumulated amortization	278,071	282,415
Nuclear fuel, net of accumulated amortization	124,533	113,645
Total property, plant and equipment	15,315,340	15,158,846
DEFERRED DEBITS
Regulatory assets (Note 4)	1,135,857	1,133,987
Operating lease right-of-use assets	501,395	503,475
Assets for pension and other postretirement benefits (Note 5)	410,933	495,673
Other	35,751	34,413
Total deferred debits	2,083,936	2,167,548
TOTAL ASSETS	20,098,687	19,924,251
CURRENT LIABILITIES
Accounts payable	301,675	311,699
Accrued taxes	211,174	148,970
Accrued interest	56,454	56,322
Common dividends payable	0	93,500
Short-term borrowings (Note 3)	199,500	0
Customer deposits	45,170	48,340
Liabilities from risk management activities (Note 7)	3,067	7,557
Liabilities for asset retirements	16,021	15,586
Operating lease liabilities	74,235	74,695
Regulatory liabilities (Note 4)	250,228	229,088
Other current liabilities	152,290	190,420
Total current liabilities	1,309,814	1,176,177
Long-term debt less current maturities (Note 3)	5,818,520	5,817,945
DEFERRED CREDITS AND OTHER
Deferred income taxes	2,150,668	2,143,673
Regulatory liabilities (Note 4)	2,427,769	2,450,169
Liabilities for asset retirements	693,383	689,497
Liabilities for pension benefits (Note 5)	147,235	148,943
Liabilities from risk management activities (Note 7)	6,928	11,062
Customer advances	220,999	221,032
Coal mine reclamation	171,227	170,097
Deferred investment tax credit	190,842	191,372
Unrecognized tax benefits	39,863	39,410
Operating lease liabilities	358,840	359,653
Other	176,324	160,036
Total deferred credits and other	6,584,078	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	3,252,244	3,216,955
Accumulated other comprehensive loss	(39,991)	(40,918)
Total shareholders’ equity	6,262,111	6,225,895
Noncontrolling interests (Note 6)	124,164	119,290
Total equity	6,386,275	6,345,185
Total capitalization	12,204,795	12,163,130
TOTAL LIABILITIES AND EQUITY	$ 20,098,687	$ 19,924,251