CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES
NET INCOME	$ 499,591	$ 481,447
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization including nuclear fuel	489,861	445,707
Deferred fuel and purchased power	(82,486)	(43,348)
Deferred fuel and purchased power amortization	92,397	(18,153)
Allowance for equity funds used during construction	(39,411)	(32,666)
Deferred income taxes	117,571	211,249
Deferred investment tax credit	(7,397)	(4,293)
Change in derivative instruments fair value	0	(254)
Stock compensation	16,140	16,553
Changes in current assets and liabilities:
Customer and other receivables	(65,203)	(206,920)
Accrued unbilled revenues	(83,939)	(44,027)
Materials, supplies and fossil fuel	(20,591)	(1,881)
Income tax receivable	0	3,751
Other current assets	23,661	(22,043)
Accounts payable	(11,399)	(24,258)
Accrued taxes	78,624	89,827
Other current liabilities	12,852	3,936
Change in margin and collateral accounts — assets	(588)	(1,826)
Change in margin and collateral accounts — liabilities	(982)	(1,625)
Change in unrecognized tax benefits	(1,235)	5,891
Change in other long-term assets	14,708	(59,963)
Change in other long-term liabilities	(72,411)	(25,180)
Net cash flow provided by operating activities	959,763	771,924
CASH FLOWS FROM INVESTING ACTIVITIES
Capital expenditures	(898,455)	(1,027,753)
Contributions in aid of construction	22,611	24,924
Allowance for borrowed funds used during construction	(18,959)	(15,378)
Proceeds from nuclear decommissioning trust sales and other special use funds	443,215	351,860
Investment in nuclear decommissioning trust and other special use funds	(461,777)	(353,001)
Other	49	(20,291)
Net cash flow used for investing activities	(913,316)	(1,039,639)
CASH FLOWS FROM FINANCING ACTIVITIES
Issuance of long-term debt	295,245	549,478
Short-term borrowing and payments — net	19,800	(68,800)
Short-term debt borrowings under revolving credit facility	45,000	23,000
Short-term debt repayments under revolving credit facility	(32,000)	0
Repayment of long-term debt	(82,000)	0
Dividends paid on common stock	(228,037)	(213,927)
Common stock equity issuance - net of purchases	(1,984)	(8,870)
Distributions to noncontrolling interests	(11,372)	(11,372)
Other	0	(1)
Net cash flow provided by financing activities	4,652	269,508
NET INCREASE IN CASH AND CASH EQUIVALENTS	51,099	1,793
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	13,892	8,881
CASH AND CASH EQUIVALENTS AT END OF PERIOD	64,991	10,674
Supplemental disclosure of cash flow information
Income taxes, net of refunds	10,091	2,185
Interest, net of amounts capitalized	161,875	147,149
Significant non-cash investing and financing activities:
Accrued capital expenditures	99,405	93,031
APS
CASH FLOWS FROM OPERATING ACTIVITIES
NET INCOME	540,409	491,143
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization including nuclear fuel	488,223	444,439
Deferred fuel and purchased power	(82,486)	(43,348)
Deferred fuel and purchased power amortization	92,397	(18,153)
Allowance for equity funds used during construction	(39,411)	(32,666)
Deferred income taxes	86,319	202,256
Deferred investment tax credit	(7,397)	(4,293)
Change in derivative instruments fair value	0	(254)
Changes in current assets and liabilities:
Customer and other receivables	(56,874)	(185,130)
Accrued unbilled revenues	(83,939)	(44,027)
Materials, supplies and fossil fuel	(20,694)	(1,755)
Income tax receivable	0	11,174
Other current assets	20,258	(19,100)
Accounts payable	(8,857)	(29,784)
Accrued taxes	106,172	102,638
Other current liabilities	9,289	11,747
Change in margin and collateral accounts — assets	(588)	(1,826)
Change in margin and collateral accounts — liabilities	(982)	(1,625)
Change in unrecognized tax benefits	(1,235)	5,891
Change in other long-term assets	25,993	(56,375)
Change in other long-term liabilities	(78,678)	(26,049)
Net cash flow provided by operating activities	987,919	804,903
CASH FLOWS FROM INVESTING ACTIVITIES
Capital expenditures	(889,347)	(1,008,723)
Contributions in aid of construction	22,611	24,924
Allowance for borrowed funds used during construction	(18,959)	(15,378)
Proceeds from nuclear decommissioning trust sales and other special use funds	443,040	351,860
Investment in nuclear decommissioning trust and other special use funds	(461,602)	(353,001)
Other	(1,261)	(18,098)
Net cash flow used for investing activities	(905,518)	(1,018,416)
CASH FLOWS FROM FINANCING ACTIVITIES
Issuance of long-term debt	295,245	549,478
Short-term borrowing and payments — net	0	(103,700)
Short-term debt borrowings under revolving credit facility	25,000	0
Short-term debt repayments under revolving credit facility	(25,000)	0
Repayment of long-term debt	(82,000)	0
Dividends paid on common stock	(233,300)	(219,100)
Distributions to noncontrolling interests	(11,372)	(11,372)
Net cash flow provided by financing activities	(31,427)	215,306
NET INCREASE IN CASH AND CASH EQUIVALENTS	50,974	1,793
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	13,851	8,840
CASH AND CASH EQUIVALENTS AT END OF PERIOD	64,825	10,633
Supplemental disclosure of cash flow information
Income taxes, net of refunds	24,746	132
Interest, net of amounts capitalized	154,788	142,779
Significant non-cash investing and financing activities:
Accrued capital expenditures	$ 99,405	$ 94,769