SCHEDULE I - CONDENSED FINANCIAL INFORMATION OF REGISTRANT - Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash Flows from Operating Activities
Net income	$ 570,052	$ 557,813	$ 530,540
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	686,253	664,140	650,955
Deferred income taxes	69,469	(1,479)	117,355
Accounts receivable	(18,191)	(12,789)	37,530
Accounts payable	(6,059)	50,641	(14,602)
Net cash flow provided by operating activities	966,365	956,726	1,277,144
Cash flows from investing activities
Net cash flow used for investing activities	(1,277,818)	(1,130,977)	(1,192,824)
Cash flows from financing activities
Issuance of long-term debt	1,596,672	1,092,188	445,245
Short-term debt borrowings under revolving credit facility	751,690	49,000	45,000
Short-term debt repayments under revolving credit facility	(770,690)	(65,000)	(57,000)
Dividends paid on common stock	(350,577)	(329,643)	(308,892)
Repayment of long-term debt	(915,150)	(600,000)	(182,000)
Common stock equity issuance and purchases — net	(1,389)	692	(5,055)
Net cash flow provided by (used for) financing activities	361,138	178,768	(92,446)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	49,685	4,517	(8,126)
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	10,283	5,766	13,892
CASH AND CASH EQUIVALENTS AT END OF YEAR	59,968	10,283	5,766
Pinnacle West
Cash Flows from Operating Activities
Net income	550,559	538,320	511,047
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in earnings of subsidiaries - net	(566,147)	(562,946)	(569,249)
Depreciation and amortization	76	76	76
Deferred income taxes	33,007	(35,831)	49,535
Accounts receivable	(7,903)	182	(7,881)
Accounts payable	(1,964)	(2,129)	1,967
Accrued taxes and income tax receivable - net	9,610	16,400	(13,535)
Dividends received from subsidiaries	357,500	336,300	316,000
Other	20,163	(1,300)	31,807
Net cash flow provided by operating activities	394,901	289,072	319,767
Cash flows from investing activities
Investments in subsidiaries	(137,881)	1,557	(142,796)
Repayments of loans from subsidiaries	932	4,190	6,477
Advances of loans to subsidiaries	(7,261)	(4,165)	(500)
Net cash flow used for investing activities	(144,210)	1,582	(136,819)
Cash flows from financing activities
Issuance of long-term debt	496,950	0	150,000
Short-term debt borrowings under revolving credit facility	211,690	49,000	20,000
Short-term debt repayments under revolving credit facility	(230,690)	(65,000)	(32,000)
Commercial paper — net	73,325	54,275	(7,000)
Dividends paid on common stock	(350,577)	(329,643)	(308,892)
Repayment of long-term debt	(450,000)	0	0
Common stock equity issuance and purchases — net	(1,389)	692	(5,055)
Other	0	0	(1)
Net cash flow provided by (used for) financing activities	(250,691)	(290,676)	(182,948)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	0	(22)	0
CASH AND CASH EQUIVALENTS AT BEGINNING OF YEAR	19	41	41
CASH AND CASH EQUIVALENTS AT END OF YEAR	$ 19	$ 19	$ 41