v3.3.1.900
Acquisitions, Divestitures and Discontinued Operations (Textuals) (Details)
$ in Millions
 9 Months Ended 12 Months Ended
Sep. 30, 2014
USD ($)
MW
Dec. 31, 2015
USD ($)
MWh
Dec. 31, 2014
USD ($)
MW
Dec. 31, 2013
USD ($)
Feb. 05, 2016
USD ($)
MW
Oct. 01, 2015
USD ($)
Jul. 03, 2014
Mar. 31, 2014
USD ($)
MW
Business Acquisition [Line Items]                
Amortization of Intangible Assets   $ 20 $ 14 $ 14        
(Gain) on sale of power plants, net   0 $ 753 $ 0        
Fore River Energy Center [Member]                
Business Acquisition [Line Items]                
Power generation capacity | MW     731          
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net     $ 530          
Guadalupe Energy Center [Member]                
Business Acquisition [Line Items]                
Power generation capacity | MW               1,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net               $ 625
Guadalupe Expansion Capacity [Member]                
Business Acquisition [Line Items]                
Power generation capacity | MW               400
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net               $ 15
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    
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net           296    
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets           240    
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment           5    
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill [1]           575    
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets           46    
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets           866    
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities           396    
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other           174    
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities           $ 570    
Amortization of Intangible Assets   $ 71            
Electricity Sales Volume | MWh   22,000,000            
Osprey Energy Center [Member]                
Business Acquisition [Line Items]                
Proceeds from Sale of Productive Assets     $ 166          
Osprey Energy Center Agreement Term     27 months          
Incremental CCFC Term Loans [Member]                
Business Acquisition [Line Items]                
Debt Instrument, Face Amount               $ 425
Six Power Plants [Member]                
Business Acquisition [Line Items]                
Proceeds from Sale of Productive Assets $ 1,570              
Ownership percentage before divestiture of business             100.00%  
Working Capital Adjustment to Sale price 2              
(Gain) on sale of power plants, net $ 753              
Columbia Energy Center [Member]                
Business Acquisition [Line Items]                
Power generation capacity | MW [2] 606              
Santa Rosa Energy Center [Member]                
Business Acquisition [Line Items]                
Power generation capacity | MW 225              
Hog Bayou Energy Center [Member]                
Business Acquisition [Line Items]                
Power generation capacity | MW 237              
Decatur Energy Center [Member]                
Business Acquisition [Line Items]                
Power generation capacity | MW 795              
Carville Energy Center [Member]                
Business Acquisition [Line Items]                
Power generation capacity | MW [2] 501              
Oneta Energy Center [Member]                
Business Acquisition [Line Items]                
Power generation capacity | MW 1,134              
Six Power Plants [Member]                
Business Acquisition [Line Items]                
Power generation capacity | MW 3,498              
Customer Relationships [Member] | Champion Energy Marketing, LLC [Member]                
Business Acquisition [Line Items]                
Finite-Lived Intangible Asset, Useful Life   7 years            
Trade Names [Member] | Champion Energy Marketing, LLC [Member]                
Business Acquisition [Line Items]                
Finite-Lived Intangible Asset, Useful Life   15 years            
Subsequent Event [Member] | Granite Ridge Energy Center [Member]                
Business Acquisition [Line Items]                
Power generation capacity | MW         745      
Summer peaking capacity | MW         695      
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net         $ 500      
[1] The intangible assets are recorded in other assets on our Consolidated Balance Sheet and consist primarily of acquired customer contracts, which are being amortized over various contract terms, and customer relationships and trade name which are being amortized over seven and 15 years, respectively. For the year ended December 31, 2015, we recorded amortization expense of $71 million related to these intangible assets.
[2] Indicates combined-cycle cogeneration power plant