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Summary of Significant Accounting and Reporting Policies - Noncontrolling Interest (Details) - USD ($)
$ in Millions
 9 Months Ended
May. 12, 2015
Sep. 30, 2015
Sep. 30, 2014
Jul. 01, 2014
Partners' Capital Attributable to Noncontrolling Interest [Roll Forward]        
Noncontrolling interest, beginning of period   $ 732 [1] $ 0  
Payments to NEE for acquisitions of projects   (716) (288)  
NEE purchase of NEP OpCo's common units $ 109 702 0  
Cash distributions   (47) 0  
Noncash distributions   (7) 0  
Noncash contributions, net   103 1,372  
Comprehensive income attributable to noncontrolling interest, including pre-acquisition net income of the 2015 acquisitions   21 14  
Noncash member contribution upon transition from predecessor method   3 (60)  
Noncontrolling interest, ending of period   $ 791 $ 1,038  
NEP OpCo [Member]        
Noncontrolling Interest [Line Items]        
Noncontrolling interest, percent ownership 22.20% 22.60%   20.10%
Noncontrolling interest, percent ownership by noncontrolling owners   79.90%    
[1] Prior-period financial information has been retrospectively adjusted as discussed in Note 2.