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Commitments and Contingencies - Environmental Matters and Financial Assurances (Details)
$ in Millions
6 Months Ended
Jul. 06, 2016
guarantee
Jun. 30, 2016
USD ($)
Letter_of_credit
Jun. 24, 2016
Mar. 16, 2016
USD ($)
May 23, 2013
USD ($)
Jun. 30, 2016
USD ($)
Letter_of_credit
Environmental Matters            
Clean power plan, optional extension period           2 years
Four Corners | New Mexico Tax Matter            
Environmental Matters            
Coal severance surtax, penalty, and interest         $ 30.0  
Litigation settlement awarded (against), amount       $ (1.0)    
Arizona Public Service Company | Letter of Credit Expiring in 2016 and 2017            
Financial Assurances            
Outstanding letters of credit   $ 79.0       $ 79.0
Arizona Public Service Company | Letters of Credit Expiring in 2017            
Financial Assurances            
Number of letters of credit expiring | Letter_of_credit   150,000,000       150,000,000
Arizona Public Service Company | Four Corners | New Mexico Tax Matter            
Environmental Matters            
Share of the assessment         12.0  
Partial payment of assessment         $ 0.8  
Litigation settlement awarded (against), amount       $ (0.8)    
4C Acquisition, LLC | Four Corners Units 4 and 5            
Environmental Matters            
Percentage of share of cost of control           7.00%
Regional Haze Rules | Arizona Public Service Company | Four Corners Units 4 and 5            
Environmental Matters            
Percentage of share of cost of control           63.00%
Expected environmental cost           $ 400.0
Regional Haze Rules | Arizona Public Service Company | Natural gas tolling contract obligations | Four Corners Units 4 and 5            
Environmental Matters            
Additional percentage share of cost of control           7.00%
Regional Haze Rules | Arizona Public Service Company | Four Corners | Four Corners Units 4 and 5            
Environmental Matters            
Site contingency increase in loss exposure not accrued, best estimate           $ 45.0
Regional Haze Rules | Arizona Public Service Company | Navajo Plant            
Environmental Matters            
Expected environmental cost           200.0
Regional Haze Rules | Arizona Public Service Company | Cholla            
Environmental Matters            
Expected environmental cost           100.0
Proposal comment period   45 days        
Mercury and air toxic standards (MATS) | Arizona Public Service Company | Navajo Plant            
Environmental Matters            
Expected environmental cost           1.0
Mercury and air toxic standards (MATS) | Arizona Public Service Company | Cholla            
Environmental Matters            
Expected environmental cost           8.0
Coal combustion waste | Arizona Public Service Company | Four Corners            
Environmental Matters            
Site contingency increase in loss exposure not accrued, best estimate           15.0
Coal combustion waste | Arizona Public Service Company | Navajo Plant            
Environmental Matters            
Site contingency increase in loss exposure not accrued, best estimate           1.0
Coal combustion waste | Arizona Public Service Company | Navajo Plant | Boron Inclusion on List of Groundwater Constituents            
Environmental Matters            
Industry litigation, period to complete rulemaking proceeding     3 years      
Coal combustion waste | Arizona Public Service Company | Cholla            
Environmental Matters            
Site contingency increase in loss exposure not accrued, best estimate           $ 40.0
Payment Guarantee | Subsequent Event            
Financial Assurances            
Number of parental guarantees | guarantee 2