CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
CURRENT ASSETS
Cash and cash equivalents	$ 181,926	$ 10,283
Customer and other receivables	417,415	266,426
Accrued unbilled revenues	175,341	128,165
Allowance for doubtful accounts	(18,069)	(8,171)
Materials and supplies (at average cost)	322,017	331,091
Fossil fuel (at average cost)	17,060	14,829
Income tax receivable	4,325	21,727
Assets from risk management activities (Note 7)	13,875	515
Deferred fuel and purchased power regulatory asset (Note 4)	162,111	70,137
Other regulatory assets (Note 4)	110,759	133,070
Other current assets	67,926	61,958
Total current assets	1,454,686	1,030,030
INVESTMENTS AND OTHER ASSETS
Nuclear decommissioning trust (Notes 11 and 12)	1,069,837	1,010,775
Other special use funds (Notes 11 and 12)	268,292	245,095
Other assets	96,855	96,953
Total investments and other assets	1,434,984	1,352,823
PROPERTY, PLANT AND EQUIPMENT
Plant in service and held for future use	20,453,437	19,836,292
Accumulated depreciation and amortization	(6,999,995)	(6,637,857)
Net	13,453,442	13,198,435
Construction work in progress	972,024	808,133
Intangible assets, net of accumulated amortization	266,220	290,564
Nuclear fuel, net of accumulated amortization	128,876	123,500
Total property, plant and equipment	14,919,565	14,522,538
DEFERRED DEBITS
Regulatory assets (Note 4)	1,305,437	1,304,073
Operating lease right-of-use assets (Note 16)	502,898	145,813
Assets for other postretirement benefits (Note 5)	105,675	90,570
Other	28,176	33,400
Total deferred debits	1,942,186	1,573,856
TOTAL ASSETS	19,751,421	18,479,247
CURRENT LIABILITIES
Current maturities of long-term debt (Note 3)	0	800,000
Accounts payable	288,265	346,448
Accrued taxes	221,358	144,899
Accrued interest	60,642	53,534
Common dividends payable	0	87,982
Short-term borrowings (Note 3)	57,925	114,675
Customer deposits	47,730	64,908
Liabilities from risk management activities (Note 7)	4,266	38,946
Liabilities for asset retirements	12,226	11,025
Operating lease liabilities (Note 16)	89,064	12,713
Regulatory liabilities (Note 4)	308,019	234,912
Other current liabilities	155,289	168,323
Total current liabilities	1,244,784	2,078,365
Long-term debt less current maturities (Note 3)	6,316,420	4,832,558
DEFERRED CREDITS AND OTHER
Deferred income taxes	2,163,050	1,992,339
Regulatory liabilities (Note 4)	2,079,323	2,267,835
Liabilities for asset retirements	674,025	646,193
Liabilities for pension benefits (Note 5)	177,855	280,185
Liabilities from risk management activities (Note 7)	9,092	33,186
Customer advances	224,924	215,330
Unrecorded Unconditional Purchase Obligation	168,997	165,695
Deferred investment tax credit	187,926	196,468
Unrecognized tax benefits	6,013	6,189
Operating lease liabilities (Note 16)	358,490	51,872
Other	173,347	159,844
Total deferred credits and other	6,223,042	6,015,136
COMMITMENTS AND CONTINGENCIES (NOTE 8)
EQUITY
Common stock, no par value; authorized 150,000,000 shares, 112,623,623 and 112,540,126 issued at respective dates	2,670,358	2,659,561
Treasury stock at cost; 33,717 and 103,546 shares at respective dates	(2,966)	(9,427)
Total common stock	2,667,392	2,650,134
Retained earnings	3,231,485	2,837,610
Accumulated other comprehensive loss	(57,491)	(57,096)
Total shareholders’ equity	5,841,386	5,430,648
Noncontrolling interests (Note 6)	125,789	122,540
Total equity	5,967,175	5,553,188
TOTAL LIABILITIES AND EQUITY	19,751,421	18,479,247
APS
CURRENT ASSETS
Cash and cash equivalents	181,793	10,169
Customer and other receivables	417,362	255,479
Accrued unbilled revenues	175,341	128,165
Allowance for doubtful accounts	(18,069)	(8,171)
Materials and supplies (at average cost)	322,017	331,091
Fossil fuel (at average cost)	17,060	14,829
Income tax receivable	0	7,313
Assets from risk management activities (Note 7)	13,875	515
Deferred fuel and purchased power regulatory asset (Note 4)	162,111	70,137
Other regulatory assets (Note 4)	110,759	133,070
Other current assets	42,847	38,895
Total current assets	1,425,096	981,492
INVESTMENTS AND OTHER ASSETS
Nuclear decommissioning trust (Notes 11 and 12)	1,069,837	1,010,775
Other special use funds (Notes 11 and 12)	268,292	245,095
Other assets	48,393	43,781
Total investments and other assets	1,386,522	1,299,651
PROPERTY, PLANT AND EQUIPMENT
Plant in service and held for future use	20,449,975	19,832,805
Accumulated depreciation and amortization	(6,996,748)	(6,634,597)
Net	13,453,227	13,198,208
Construction work in progress	972,024	808,133
Intangible assets, net of accumulated amortization	266,065	290,409
Nuclear fuel, net of accumulated amortization	128,876	123,500
Total property, plant and equipment	14,919,195	14,522,156
DEFERRED DEBITS
Regulatory assets (Note 4)	1,305,437	1,304,073
Operating lease right-of-use assets (Note 16)	501,282	144,024
Assets for other postretirement benefits (Note 5)	101,792	86,736
Other	27,592	32,591
Total deferred debits	1,936,103	1,567,424
TOTAL ASSETS	19,666,916	18,370,723
CURRENT LIABILITIES
Current maturities of long-term debt (Note 3)	0	350,000
Accounts payable	282,868	338,006
Accrued taxes	268,990	136,328
Accrued interest	58,403	52,619
Common dividends payable	0	88,000
Customer deposits	47,730	64,908
Liabilities from risk management activities (Note 7)	4,266	38,946
Liabilities for asset retirements	12,226	11,025
Operating lease liabilities (Note 16)	88,975	12,549
Regulatory liabilities (Note 4)	308,019	234,912
Other current liabilities	153,986	164,736
Total current liabilities	1,225,463	1,492,029
Long-term debt less current maturities (Note 3)	5,820,303	4,833,133
DEFERRED CREDITS AND OTHER
Deferred income taxes	2,166,599	2,033,096
Regulatory liabilities (Note 4)	2,079,323	2,267,835
Liabilities for asset retirements	674,025	646,193
Liabilities for pension benefits (Note 5)	161,186	262,243
Liabilities from risk management activities (Note 7)	9,092	33,186
Customer advances	224,924	215,330
Unrecorded Unconditional Purchase Obligation	168,997	165,695
Deferred investment tax credit	187,926	196,468
Unrecognized tax benefits	39,589	40,188
Operating lease liabilities (Note 16)	356,783	50,092
Other	142,431	136,432
Total deferred credits and other	6,210,875	6,046,758
COMMITMENTS AND CONTINGENCIES (NOTE 8)
EQUITY
Common stock	178,162	178,162
Additional paid-in capital	2,721,696	2,721,696
Retained earnings	3,418,753	3,011,927
Accumulated other comprehensive loss	(34,125)	(35,522)
Total shareholders’ equity	6,284,486	5,876,263
Noncontrolling interests (Note 6)	125,789	122,540
Total equity	6,410,275	5,998,803
Total capitalization	12,230,578	10,831,936
TOTAL LIABILITIES AND EQUITY	19,666,916	18,370,723
Variable Interest Entity
PROPERTY, PLANT AND EQUIPMENT
Total property, plant and equipment	99,003	101,906
Variable Interest Entity | APS
PROPERTY, PLANT AND EQUIPMENT
Total property, plant and equipment	99,003	101,906
EQUITY
Noncontrolling interests (Note 6)	$ 125,789	$ 122,540