Annual report pursuant to Section 13 and 15(d)

The Company - Schedule of Investments in Equity Method Affiliates (Detail)

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The Company - Schedule of Investments in Equity Method Affiliates (Detail) - USD ($)
$ in Millions
Dec. 31, 2015
Aug. 31, 2015
Jun. 30, 2015
May. 31, 2015
Apr. 30, 2015
Oct. 31, 2014
Strong Upwind Holdings I, LLC [Member] | JPMorgan [Member]            
Schedule of Equity Method Investments [Line Items]            
Project investment amount     $ 141 $ 144    
Strong Upwind Holdings I, LLC [Member] | JPMorgan [Member] | Wind Projects [Member]            
Schedule of Equity Method Investments [Line Items]            
Project investment amount           $ 141
Strong Upwind Holdings II, LLC [Member] | JPMorgan [Member] | Wind Projects [Member]            
Schedule of Equity Method Investments [Line Items]            
Project investment amount         $ 36  
Creston Ridge Management, LLC [Member] | Bluestem [Member] | Wind Projects [Member]            
Schedule of Equity Method Investments [Line Items]            
Project investment amount   $ 13        
Strong Upwind Holdings III, LLC [Member] | JPMorgan [Member] | Wind Projects [Member]            
Schedule of Equity Method Investments [Line Items]            
Project investment amount $ 84          
Buckeye Wind Energy Class B Holdings LLC [Member] | Invenergy [Member] | Wind Projects [Member]            
Schedule of Equity Method Investments [Line Items]            
Project investment amount $ 71