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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.

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