Business Acquisitions - Additional Information (Details)									1 Months Ended	12 Months Ended
	Jun. 19, 2018 USD ($)	May 31, 2018 USD ($)	Apr. 18, 2018 USD ($) MW	Mar. 31, 2018 USD ($)	Nov. 02, 2017 USD ($)	Aug. 02, 2017 USD ($)	Mar. 27, 2017 USD ($) MW	Sep. 02, 2016 USD ($)	Jan. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) MW	Dec. 31, 2017 USD ($)		Dec. 31, 2016 USD ($)	[1]	Mar. 30, 2018 USD ($) MW	Nov. 01, 2017 USD ($) MW	Aug. 01, 2017 USD ($)	Sep. 01, 2016 USD ($)	Aug. 31, 2016	Nov. 03, 2015 USD ($)
Business Acquisition [Line Items]
Ownership interest acquired															100.00%
Long-term debt										$ 6,044,000,000	$ 6,083,000,000
Proceeds from noncontrolling interests										91,000,000	13,000,000	[1]	$ 5,000,000
Non-recourse debt										$ 878,000,000
Central CA Fuel Cell 1 [Member]
Business Acquisition [Line Items]
UPMC thermal project cash considerations			$ 11,000,000
Power generation gapacity, megawatts | MW			2.8
Power purchase agreement period			20 years
Buckthorn Solar Drop Down Asset
Business Acquisition [Line Items]
UPMC thermal project cash considerations				$ 42,000,000
Power generation gapacity, megawatts | MW															154
Power purchase agreement period										25 years
Non-controlling interest				19,000,000
Allocations of taxable income from tax equity investor										$ 0.99
Taxable income allocation, pre-flip										67.00%
Taxable income allocation, post-flip										99.00%
Allocations of investor change percent										5.00%
Net assets acquired				$ 25,000,000
UPMC Thermal
Business Acquisition [Line Items]
UPMC thermal project cash considerations	$ 84,000,000
CVSR
Business Acquisition [Line Items]
UPMC thermal project cash considerations								$ 78,500,000
Ownership interest acquired																		51.05%
Ownership percentage																			48.95%
Historical value								112,000,000
Additional debt																		$ 496,000,000
AOCL								$ 6,000,000
Percentage of debt consolidated																		100.00%
August 2017 Drop Down Assets
Business Acquisition [Line Items]
UPMC thermal project cash considerations						$ 44,000,000
Ownership interest acquired																	25.00%			75.00%
Contingent consideration																	$ 8,000,000
Business acquisition, percentage of assets recorded as noncontrolling interest																				25.00%
Net assets acquired																				$ 87,000,000
November 2017 Drop Down Assets
Business Acquisition [Line Items]
UPMC thermal project cash considerations					$ 74,000,000
Power generation gapacity, megawatts | MW																38
Long-term debt																$ 26,000,000
Buckthorn Solar, due 2025
Business Acquisition [Line Items]
Long-term debt		$ 132,000,000								$ 132,000,000	169,000,000
Buckthorn Solar, due 2025 | Buckthorn Solar Drop Down Asset
Business Acquisition [Line Items]
Long-term debt															$ 183,000,000
CVSR Financing Agreement
Business Acquisition [Line Items]
Long-term debt										720,000,000	746,000,000
CVSR Financing Agreement | CVSR
Business Acquisition [Line Items]
Long-term debt																		$ 771,000,000
CVSR Holdco due 2037
Business Acquisition [Line Items]
Long-term debt										$ 188,000,000	$ 194,000,000
CVSR Holdco due 2037 | CVSR
Business Acquisition [Line Items]
Long-term debt																		$ 200,000,000
Agua Caliente Borrower 2
Business Acquisition [Line Items]
Power generation gapacity, megawatts | MW							46
Power purchase agreement period							25 years
Ownership percentage										16.00%
Percentage of NRG's ownership							31.00%
Remaining power purchase agreement term							22 years
Non-recourse debt							$ 41,000,000
Utah Portfolio
Business Acquisition [Line Items]
Ownership percentage										50.00%
Remaining power purchase agreement term							20 years
Net working capital adjustment										$ 106,000,000
Non-recourse debt							$ 287,000,000
March 2017 Drop Down Assets
Business Acquisition [Line Items]
UPMC thermal project cash considerations							128,000,000
Net working capital adjustment										$ 3,000,000
Historical value							$ 8,000,000
Buckthorn Solar Drop Down Asset
Business Acquisition [Line Items]
Proceeds from noncontrolling interests		$ 80,000,000
NRG | Agua Caliente Borrower 2
Business Acquisition [Line Items]
Percentage of ownership							51.00%
Thermal
Business Acquisition [Line Items]
Steam and chilled water capacity, megawatts thermal equivalent | MW										1,385
Power generation gapacity, megawatts | MW										133
Thermal | UPMC Thermal
Business Acquisition [Line Items]
Steam and chilled water capacity, megawatts thermal equivalent | MW										73
Power generation gapacity, megawatts | MW										7.5
Subsequent Event | UPMC Thermal
Business Acquisition [Line Items]
UPMC thermal project cash considerations									$ 3,000,000

[1] Retrospectively adjusted as discussed in Note 1, Nature of Business.