Annual report pursuant to Section 13 and 15(d)

Our Portfolio - Schedule of Equity Method Investments (Detail)

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Our Portfolio - Schedule of Equity Method Investments (Detail) - USD ($)
$ in Millions
Dec. 31, 2017
Oct. 31, 2016
Jun. 30, 2016
Dec. 31, 2015
Schedule of Equity Method Investments [Line Items]        
Projects investment amount $ 523      
Northern Frontier LLC [Member] | NextEra Energy [Member] | Renewable Energy Projects [Member]        
Schedule of Equity Method Investments [Line Items]        
Projects investment amount 127      
Vento I, LLC [Member] | EDP Renewables [Member] | Renewable Energy Projects [Member]        
Schedule of Equity Method Investments [Line Items]        
Projects investment amount 119      
Buckeye Wind Energy Class B Holdings LLC [Member] | Invenergy [Member] | Renewable Energy Projects [Member]        
Schedule of Equity Method Investments [Line Items]        
Projects investment amount       $ 68
Invenergy Gunsight Mountain Holdings LLC [Member] | Invenergy [Member] | Renewable Energy Projects [Member]        
Schedule of Equity Method Investments [Line Items]        
Projects investment amount   $ 37    
MM Solar Parent LLC [Member] | AES [Member] | Renewable Energy Projects [Member]        
Schedule of Equity Method Investments [Line Items]        
Projects investment amount     $ 29  
Helix Fund Vento I, LLC [Member] | Various [Member] | Renewable Energy Projects [Member]        
Schedule of Equity Method Investments [Line Items]        
Projects investment amount     $ 25  
Other Transactions [Member] | Various [Member] | Renewable Energy Projects [Member]        
Schedule of Equity Method Investments [Line Items]        
Projects investment amount $ 118