Segment Reporting (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Mar. 27, 2017	Dec. 31, 2016	Sep. 01, 2016
Segment Reporting Information
Operating revenues	$ 2,701	$ 2,248	$ 5,083	$ 4,907
Depreciation and amortization	260	262	517	528
Impairment losses	63	56	63	56
Equity in earnings/(losses) of unconsolidated affiliates	(3)	4	2	(3)
Gain/(loss) on sale of assets	2	(83)	4	(83)
Impairment loss on investment				(139)
Loss on debt extinguishment, net	0	(80)	(2)	(69)
Income/(Loss) before income taxes	103	(138)	(71)	(173)
Loss from continuing operations	99	(163)	(70)	(220)
Loss from discontinued operations, net of income tax	(741)	(113)	(775)	(9)
Net Income/(Loss)	(642)	(276)	(845)	(229)
Net loss attributable to NRG Energy, Inc.	(626)	(271)	(790)	(189)
Total assets	25,205		25,205			$ 30,682
Renewables
Segment Reporting Information
Impairment losses	22
Operating Segments | Generation/Business
Segment Reporting Information
Operating revenues	882	504	1,848	1,637
Depreciation and amortization	95	97	192	197
Impairment losses	41	17	41	17
Equity in earnings/(losses) of unconsolidated affiliates	(15)	2	(28)	(5)
Gain/(loss) on sale of assets		0		0
Impairment loss on investment				(137)
Loss on debt extinguishment, net		0		0
Income/(Loss) before income taxes	(89)	(458)	(54)	(433)
Loss from continuing operations	(90)	(458)	(56)	(433)
Loss from discontinued operations, net of income tax	0	0	0	0
Net Income/(Loss)	(90)	(458)	(56)	(433)
Net loss attributable to NRG Energy, Inc.	(90)	(458)	(56)	(433)
Total assets	8,539		8,539
Operating Segments | Retail
Segment Reporting Information
Operating revenues	1,603	1,536	2,938	2,906
Depreciation and amortization	29	29	57	57
Impairment losses	0	0	0	0
Equity in earnings/(losses) of unconsolidated affiliates	0	0	0	0
Gain/(loss) on sale of assets		0		0
Impairment loss on investment				0
Loss on debt extinguishment, net		0		0
Income/(Loss) before income taxes	330	657	303	808
Loss from continuing operations	341	657	311	807
Loss from discontinued operations, net of income tax	0	0	0	0
Net Income/(Loss)	341	657	311	807
Net loss attributable to NRG Energy, Inc.	341	661	311	807
Total assets	2,439		2,439
Operating Segments | Renewables
Segment Reporting Information
Operating revenues	123	101	220	197
Depreciation and amortization	50	47	99	95
Impairment losses	22	27	22	27
Equity in earnings/(losses) of unconsolidated affiliates	(2)	(2)	(3)	(8)
Gain/(loss) on sale of assets		0		0
Impairment loss on investment				0
Loss on debt extinguishment, net		0		0
Income/(Loss) before income taxes	(52)	(75)	(89)	(122)
Loss from continuing operations	(47)	(71)	(79)	(111)
Loss from discontinued operations, net of income tax	0	0	0	0
Net Income/(Loss)	(47)	(71)	(79)	(111)
Net loss attributable to NRG Energy, Inc.	(22)	(66)	(26)	(96)
Total assets	5,193		5,193
Operating Segments | NRG Yield
Segment Reporting Information
Operating revenues	284	283	502	517
Depreciation and amortization	78	75	153	149
Impairment losses	0	0	0	0
Equity in earnings/(losses) of unconsolidated affiliates	16	14	35	18
Gain/(loss) on sale of assets		0		0
Impairment loss on investment				0
Loss on debt extinguishment, net		0		0
Income/(Loss) before income taxes	53	76	51	78
Loss from continuing operations	45	64	44	66
Loss from discontinued operations, net of income tax	0	0		0
Net Income/(Loss)	45	64	44	66
Net loss attributable to NRG Energy, Inc.	50	48	58	58
Total assets	8,513		8,513
Operating Segments | Corporate
Segment Reporting Information
Operating revenues	3	10	11	28
Depreciation and amortization	8	14	16	30
Impairment losses	0	12	0	12
Equity in earnings/(losses) of unconsolidated affiliates	3	27	7	6
Gain/(loss) on sale of assets		(83)		(83)
Impairment loss on investment				(2)
Loss on debt extinguishment, net		(80)		(69)
Income/(Loss) before income taxes	(135)	(295)	(273)	(495)
Loss from continuing operations	(146)	(312)	(281)	(540)
Loss from discontinued operations, net of income tax	(741)	(113)	(775)	(9)
Net Income/(Loss)	(887)	(425)	(1,056)	(549)
Net loss attributable to NRG Energy, Inc.	(920)	(449)	(1,089)	(558)
Total assets	10,954		10,954
Eliminations
Segment Reporting Information
Operating revenues	(194)	(186)	(436)	(378)
Depreciation and amortization	0	0		0
Impairment losses	0	0	0	0
Equity in earnings/(losses) of unconsolidated affiliates	(5)	(37)	(9)	(14)
Gain/(loss) on sale of assets		0		0
Impairment loss on investment				0
Loss on debt extinguishment, net		0		0
Income/(Loss) before income taxes	(4)	(43)	(9)	(9)
Loss from continuing operations	(4)	(43)	(9)	(9)
Loss from discontinued operations, net of income tax	0	0		0
Net Income/(Loss)	(4)	(43)	(9)	(9)
Net loss attributable to NRG Energy, Inc.	15	(7)	12	33
Total assets	(10,433)		(10,433)
Eliminations | Generation/Business
Segment Reporting Information
Operating revenues	(171)	(166)	(406)	(330)
Eliminations | Retail
Segment Reporting Information
Operating revenues	(1)	(1)	(11)	(5)
Eliminations | Renewables
Segment Reporting Information
Operating revenues	(10)	(4)	(4)	(8)
Eliminations | NRG Yield
Segment Reporting Information
Operating revenues	(3)	(2)	0	(6)
Eliminations | Corporate
Segment Reporting Information
Operating revenues	$ (9)	$ (13)	$ (15)	$ (29)
CVSR
Segment Reporting Information
Percentage of ownership sold of subsidiary							51.05%
Agua Caliente
Segment Reporting Information
Percentage of ownership sold of subsidiary					16.00%