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Summary of Significant Accounting and Reporting Policies - Narrative (Details)
$ in Millions
 3 Months Ended
Mar. 31, 2018
USD ($)
wind_generation_facility
solar_generation_facility
MW
Mar. 31, 2017
USD ($)
 [2]
Jan. 01, 2018
USD ($)
Dec. 31, 2017
USD ($)
Property, Plant and Equipment [Line Items]        
Restricted cash, noncurrent $ 20     $ 19
Net income (loss) attributable to noncontrolling interest [1] (100) $ 46    
Accounting Standards Update 2017-05 [Member]        
Property, Plant and Equipment [Line Items]        
Net income (loss) attributable to noncontrolling interest 211      
Income (loss) attributable to noncontrolling interest, before tax 231      
Accounting Standards Update 2017-05 [Member] | Deferral Related to Differential Membership Interest - VIE [Member]        
Property, Plant and Equipment [Line Items]        
Cumulative effect of new accounting principle in period of adoption     $ 1,442  
Third-Party Investors [Member]        
Property, Plant and Equipment [Line Items]        
Net income (loss) attributable to noncontrolling interest $ 38      
NEP OpCo [Member]        
Property, Plant and Equipment [Line Items]        
Noncontrolling interest, ownership percentage by parent 34.90%      
Noncontrolling interest, ownership percentage by noncontrolling owners 65.10%      
Non Affiliated Party [Member]        
Property, Plant and Equipment [Line Items]        
Noncontrolling interest, ownership percentage by noncontrolling owners 10.00%      
Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations [Member]        
Property, Plant and Equipment [Line Items]        
Number of wind generation facilities | wind_generation_facility 4      
Number of solar generation facilities | solar_generation_facility 2      
Generation facility capacity | MW 396      
[1] For the three months ended March 31, 2017, net income attributable to noncontrolling interests includes the pre-acquisition net income of the common control acquisitions. See Note 1.
[2] Prior-period financial information has been retrospectively adjusted as discussed in Note 1.