v3.6.0.2
Acquisitions, Divestitures and Discontinued Operations (Textuals) (Details)
$ / shares in Units, $ in Millions
 3 Months Ended 9 Months Ended 12 Months Ended
Mar. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Jun. 30, 2016
USD ($)
Sep. 30, 2014
USD ($)
MW
Dec. 31, 2016
USD ($)
$ / shares
Dec. 31, 2015
USD ($)
$ / shares
MW
Dec. 31, 2014
USD ($)
Jan. 17, 2017
USD ($)
Dec. 01, 2016
USD ($)
Oct. 26, 2016
MW
Apr. 01, 2016
USD ($)
MW
Feb. 05, 2016
USD ($)
MW
Oct. 01, 2015
USD ($)
Jul. 03, 2014
MW
Mar. 31, 2014
USD ($)
MW
Business Acquisition [Line Items]                              
Business Acquisition, Pro Forma Revenue         $ 8,324 $ 8,308                  
Business Acquisition, Pro Forma Net Income (Loss)         $ 105 $ 132                  
Business Acquisition, Pro Forma Earnings Per Share, Basic | $ / shares         $ 0.30 $ 0.36                  
Business Acquisition, Pro Forma Earnings Per Share, Diluted | $ / shares         $ 0.29 $ 0.36                  
Amortization of Intangible Assets         $ 218 $ 91 $ 20                
(Gain) on sale of power plants, net         $ 157 0 $ 753                
Oneta Energy Center [Member]                              
Business Acquisition [Line Items]                              
Power generation capacity | MW       1,134                      
Carville Energy Center [Member]                              
Business Acquisition [Line Items]                              
Power generation capacity | MW [1]       501                      
Decatur Energy Center [Member]                              
Business Acquisition [Line Items]                              
Power generation capacity | MW       795                      
Hog Bayou Energy Center [Member]                              
Business Acquisition [Line Items]                              
Power generation capacity | MW       237                      
Santa Rosa Energy Center [Member]                              
Business Acquisition [Line Items]                              
Power generation capacity | MW       225                      
Columbia Energy Center [Member]                              
Business Acquisition [Line Items]                              
Power generation capacity | MW [1]       606                      
Six Power Plants [Member]                              
Business Acquisition [Line Items]                              
Power generation capacity | MW       3,498                      
Calpine Solutions [Member]                              
Business Acquisition [Line Items]                              
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net                 $ 1,150            
Working Capital Adjustment to Sale price   $ 350                          
Recovered collateral subsequent to closing   250                          
Expected recovery through collateral synergies                 $ 200            
Number of States in which Entity Operates                 19            
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net                 $ 800            
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets                 141            
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Prepaid Expense and Other Assets                 518            
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Derivative assets, current                 365            
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment                 7            
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles                 360            
Business Acquisition, Goodwill, Expected Tax Deductible Amount                 162            
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Long-term derivative assets                 359            
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets                 1,912            
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities                 276            
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Derivative liabilities, current                 270            
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Long-term derivative liabilities                 216            
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities                 762            
Granite Ridge Energy Center [Member]                              
Business Acquisition [Line Items]                              
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net                       $ 500      
Power generation capacity | MW                       745      
Summer peaking capacity | MW                       695      
Fore River Energy Center [Member]                              
Business Acquisition [Line Items]                              
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net           $ 530                  
Power generation capacity | MW           731                  
Guadalupe Energy Center [Member]                              
Business Acquisition [Line Items]                              
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net                             $ 625
Power generation capacity | MW                             1,000
Guadalupe Expansion Capacity [Member]                              
Business Acquisition [Line Items]                              
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net                             $ 15
Power generation capacity | MW                             400
Crane Champion Holdco, LLC [Member]                              
Business Acquisition [Line Items]                              
Ownership Percentage of Acquiree                         75.00%    
EDF Trading North America, LLC [Member]                              
Business Acquisition [Line Items]                              
Ownership Percentage of Acquiree                         25.00%    
Champion Energy Marketing, LLC [Member]                              
Business Acquisition [Line Items]                              
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net                         $ 240    
Osprey Energy Center [Member]                              
Business Acquisition [Line Items]                              
Osprey Energy Center Agreement Term           27 months                  
Mankato [Member]                              
Business Acquisition [Line Items]                              
Power generation capacity | MW                   375          
Proceeds from Sale of Productive Assets   396                          
Gain (Loss) on Sale of Assets and Asset Impairment Charges   $ 157                          
Expansion generation capacity | MW                   345          
South Point Energy Center [Member]                              
Business Acquisition [Line Items]                              
Summer peaking capacity | MW                     504        
Proceeds from Sale of Productive Assets     $ 76                        
Net present value of transmission capacity payment obligations                     $ 112        
Remaining tribal lease costs                     9        
Near-term repairs, maintenance and capital improvements to restore the power plant to full capacity                     $ 21        
Incremental CCFC Term Loans [Member]                              
Business Acquisition [Line Items]                              
Debt Instrument, Face Amount                             $ 425
Six Power Plants [Member]                              
Business Acquisition [Line Items]                              
Working Capital Adjustment to Sale price       $ 2                      
Power generation capacity | MW                           3,498  
Proceeds from Sale of Productive Assets       1,570                      
Ownership percentage before divestiture of business                           100.00%  
(Gain) on sale of power plants, net       $ 753                      
Acquired contracts [Member] | Calpine Solutions [Member]                              
Business Acquisition [Line Items]                              
Finite-Lived Intangible Asset, Useful Life   5 years                          
Customer Relationships [Member] | Calpine Solutions [Member]                              
Business Acquisition [Line Items]                              
Finite-Lived Intangible Asset, Useful Life   14 years                          
Subsequent Event [Member] | North American Power [Member]                              
Business Acquisition [Line Items]                              
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net               $ 105              
Ownership Percentage of Acquiree               100.00%              
Subsequent Event [Member] | Osprey Energy Center [Member]                              
Business Acquisition [Line Items]                              
Proceeds from Sale of Productive Assets $ 166                            
West [Member] | Calpine Solutions [Member]                              
Business Acquisition [Line Items]                              
Business Acquisition, Goodwill, Expected Tax Deductible Amount                 68            
Texas [Member] | Calpine Solutions [Member]                              
Business Acquisition [Line Items]                              
Business Acquisition, Goodwill, Expected Tax Deductible Amount                 15            
East [Member] | Calpine Solutions [Member]                              
Business Acquisition [Line Items]                              
Business Acquisition, Goodwill, Expected Tax Deductible Amount                 $ 79            
[1] Indicates combined-cycle cogeneration power plant.