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Long-Term Debt and Liquidity Matters - Components of Long-Term Debt (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Nov. 30, 2017
Dec. 31, 2016
Long-Term Debt and Liquidity Matters [Line Items]      
Total long-term debt $ 4,871,713   $ 4,146,785
Long-term debt less current maturities 4,789,713   4,021,785
Pinnacle West      
Long-Term Debt and Liquidity Matters [Line Items]      
Gross long-term debt 4,908,125    
Unamortized discount (184)   0
Unamortized debt issue costs (1,395)   0
Total long-term debt 298,421   125,000
Less current maturities 0   125,000
Total long-term debt less current maturities 298,421   0
Long-term debt less current maturities 298,421   0
APS      
Long-Term Debt and Liquidity Matters [Line Items]      
Gross long-term debt 4,608,125    
Unamortized discount (11,288)   (11,816)
Unamortized premium 8,049   4,506
Unamortized debt issue costs (31,594)   (29,030)
Total long-term debt 4,573,292   4,021,785
Less current maturities 82,000   0
Total long-term debt less current maturities 4,491,292   4,021,785
Pollution Control Bonds - Variable | APS      
Long-Term Debt and Liquidity Matters [Line Items]      
Gross long-term debt $ 35,975   $ 35,975
Pollution Control Bonds - Variable | APS | Minimum      
Long-Term Debt and Liquidity Matters [Line Items]      
Weighted-average interest rate (as a percent) 1.77%   0.81%
Pollution Control Bonds - Fixed | APS      
Long-Term Debt and Liquidity Matters [Line Items]      
Gross long-term debt $ 147,150   $ 147,150
Pollution Control Bonds - Fixed | APS | Minimum      
Long-Term Debt and Liquidity Matters [Line Items]      
Interest rate (as a percent) 1.75%   1.75%
Pollution Control Bonds - Fixed | APS | Maximum      
Long-Term Debt and Liquidity Matters [Line Items]      
Interest rate (as a percent) 4.70%   4.70%
Total Pollution Control Bonds | APS      
Long-Term Debt and Liquidity Matters [Line Items]      
Gross long-term debt $ 183,125   $ 183,125
Senior unsecured notes | APS      
Long-Term Debt and Liquidity Matters [Line Items]      
Gross long-term debt $ 4,275,000   $ 3,725,000
Senior unsecured notes | APS | Minimum      
Long-Term Debt and Liquidity Matters [Line Items]      
Interest rate (as a percent) 2.20%   2.20%
Senior unsecured notes | APS | Maximum      
Long-Term Debt and Liquidity Matters [Line Items]      
Interest rate (as a percent) 8.75%   8.75%
Term loan facility | Pinnacle West      
Long-Term Debt and Liquidity Matters [Line Items]      
Gross long-term debt $ 0   $ 125,000
Weighted-average interest rate (as a percent)     1.52%
Senior unsecured notes | Pinnacle West      
Long-Term Debt and Liquidity Matters [Line Items]      
Gross long-term debt $ 300,000   $ 0
Interest rate (as a percent) 2.25% 2.25%  
Term loan | APS      
Long-Term Debt and Liquidity Matters [Line Items]      
Weighted-average interest rate (as a percent) 2.236%   1.427%
Term loan | Term loans | APS      
Long-Term Debt and Liquidity Matters [Line Items]      
Term loans $ 150,000   $ 150,000