|**Earnings Per Share**                                              | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
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|**Earnings Per Share [Abstract]**                                   |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Earnings Per Share                                                  | Earnings Per ShareThe following table presents the calculation of Pinnacle West’s basic and diluted earnings per share for thethree and nine months ended September 30, 2018and2017(in thousands, except per share amounts):Three Months Ended  September 30,Nine Months Ended  September 30,2018201720182017Net income attributable to common shareholders$315,012$276,072$484,971$466,827Weighted average common shares outstanding — basic112,148111,835112,094111,787Net effect of dilutive securities:Contingently issuable performance shares and restricted stock units385566405527Weighted average common shares outstanding — diluted112,533112,401112,499112,314Earnings per weighted-average common share outstandingNet income attributable to common shareholders — basic$2.81$2.47$4.33$4.18Net income attributable to common shareholders — diluted$2.80$2.46$4.31$4.16
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|                                                                    | Three Months Ended  September 30,                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|                                                                    | 2018                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  
|Net income attributable to common shareholders                      | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Weighted average common shares outstanding — basic                  | 112,148                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Net effect of dilutive securities:                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Contingently issuable performance shares and restricted stock units | 385                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|Weighted average common shares outstanding — diluted                | 112,533                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Earnings per weighted-average common share outstanding              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
|Net income attributable to common shareholders — basic              | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|Net income attributable to common shareholders — diluted            | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     

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