Condensed Consolidating Financial Information - STATEMENTS OF OPERATIONS (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Operating Revenues
Total operating revenues	$ 2,701	$ 2,248	$ 5,083	$ 4,907
Operating Costs and Expenses
Cost of operations	1,837	1,443	3,696	3,271
Depreciation and amortization	260	262	517	528
Impairment losses	63	56	63	56
Selling, general and administrative	223	266	482	520
Acquisition-related transaction and integration costs	1	5	2	6
Development activity expenses	18	18	35	44
Total operating costs and expenses	2,402	2,050	4,795	4,425
Other income - affiliate	42	48	90	96
Gain/(loss) on sale of assets	2	(83)	4	(83)
Operating Income/(Loss)	343	163	382	495
Other Income/(Expense)
Equity in earnings/(losses) of consolidated subsidiaries	0	0	0	0
Equity in (losses)/earnings of unconsolidated affiliates	(3)	4	2	(3)
Gain/(impairment loss) on investment	0	7	0	(139)
Other income	10	5	18	22
Loss on debt extinguishment, net	0	(80)	(2)	(69)
Interest expense	(247)	(237)	(471)	(479)
Total other expense	(240)	(301)	(453)	(668)
Income/(Loss) from Continuing Operations Before Income Taxes	103	(138)	(71)	(173)
Income tax expense/(benefit)	4	25	(1)	47
Income/(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)
Less: Net (loss)/income attributable to noncontrolling interest and redeemable noncontrolling interests	(16)	(5)	(55)	(40)
Net Income/(Loss) Attributable to NRG Energy, Inc.	(626)	(271)	(790)	(189)
Eliminations
Operating Revenues
Total operating revenues	(46)	(37)	(125)	(58)
Operating Costs and Expenses
Cost of operations	(44)	(37)	(125)	(61)
Depreciation and amortization	0	0	0	0
Impairment losses	0	0	0	0
Selling, general and administrative	(1)	0	(2)	0
Acquisition-related transaction and integration costs	0	0	0	0
Development activity expenses	0	0	0	0
Total operating costs and expenses	(45)	(37)	(127)	(61)
Other income - affiliate	0		0
Gain/(loss) on sale of assets	0	0	0	0
Operating Income/(Loss)	(1)	0	2	3
Other Income/(Expense)
Equity in earnings/(losses) of consolidated subsidiaries	88	18	125	(191)
Equity in (losses)/earnings of unconsolidated affiliates	(34)	(46)	(36)	(55)
Gain/(impairment loss) on investment		0		0
Other income	0	0	0	(1)
Loss on debt extinguishment, net		0	0	0
Interest expense		0	0	0
Total other expense	54	(28)	89	(247)
Income/(Loss) from Continuing Operations Before Income Taxes	53	(28)	91	(244)
Income tax expense/(benefit)	0	0	0	0
Income/(Loss) from Continuing Operations	53	(28)	91	(244)
Loss from discontinued operations, net of income tax	0		0
Net Income/(Loss)	53	(28)	91	(244)
Less: Net (loss)/income attributable to noncontrolling interest and redeemable noncontrolling interests	(35)	(46)	(34)	(53)
Net Income/(Loss) Attributable to NRG Energy, Inc.	88	18	125	(191)
Guarantor Subsidiaries
Operating Revenues
Total operating revenues	1,758	1,716	3,357	3,655
Operating Costs and Expenses
Cost of operations	1,307	1,128	2,568	2,559
Depreciation and amortization	102	112	203	225
Impairment losses	42	0	42	0
Selling, general and administrative	86	93	184	191
Acquisition-related transaction and integration costs	0	0	0	0
Development activity expenses	0	0	0	0
Total operating costs and expenses	1,537	1,333	2,997	2,975
Other income - affiliate	0		0
Gain/(loss) on sale of assets	2	0	4	0
Operating Income/(Loss)	223	383	364	680
Other Income/(Expense)
Equity in earnings/(losses) of consolidated subsidiaries	57	(50)	(20)	(81)
Equity in (losses)/earnings of unconsolidated affiliates	0	2	0	3
Gain/(impairment loss) on investment		0		0
Other income	0	1	1	2
Loss on debt extinguishment, net		0	0	0
Interest expense	(4)	(4)	(7)	(7)
Total other expense	53	(51)	(26)	(83)
Income/(Loss) from Continuing Operations Before Income Taxes	276	332	338	597
Income tax expense/(benefit)	113	128	131	228
Income/(Loss) from Continuing Operations	163	204	207	369
Loss from discontinued operations, net of income tax	0		0
Net Income/(Loss)	163	204	207	369
Less: Net (loss)/income attributable to noncontrolling interest and redeemable noncontrolling interests	0	0	0	0
Net Income/(Loss) Attributable to NRG Energy, Inc.	163	204	207	369
Non-Guarantor Subsidiaries
Operating Revenues
Total operating revenues	989	569	1,851	1,310
Operating Costs and Expenses
Cost of operations	558	342	1,222	754
Depreciation and amortization	150	144	298	291
Impairment losses	21	56	21	56
Selling, general and administrative	38	46	84	95
Acquisition-related transaction and integration costs	1	0	2	0
Development activity expenses	13	13	25	32
Total operating costs and expenses	781	601	1,652	1,228
Other income - affiliate	0		0
Gain/(loss) on sale of assets	0	0	0	0
Operating Income/(Loss)	208	(32)	199	82
Other Income/(Expense)
Equity in earnings/(losses) of consolidated subsidiaries	(22)	(35)	(57)	(70)
Equity in (losses)/earnings of unconsolidated affiliates	676	41	707	39
Gain/(impairment loss) on investment		0		(139)
Other income	7	2	12	19
Loss on debt extinguishment, net		(4)	(2)	(4)
Interest expense	(121)	(101)	(225)	(207)
Total other expense	540	(97)	435	(362)
Income/(Loss) from Continuing Operations Before Income Taxes	748	(129)	634	(280)
Income tax expense/(benefit)	267	(33)	237	(94)
Income/(Loss) from Continuing Operations	481	(96)	397	(186)
Loss from discontinued operations, net of income tax	(741)	(116)	(775)	(15)
Net Income/(Loss)	(260)	(212)	(378)	(201)
Less: Net (loss)/income attributable to noncontrolling interest and redeemable noncontrolling interests	(9)	10	(46)	(23)
Net Income/(Loss) Attributable to NRG Energy, Inc.	(251)	(222)	(332)	(178)
NRG Energy, Inc. (Note Issuer)
Operating Revenues
Total operating revenues	0	0	0	0
Operating Costs and Expenses
Cost of operations	16	10	31	19
Depreciation and amortization	8	6	16	12
Impairment losses	0	0	0	0
Selling, general and administrative	100	127	216	234
Acquisition-related transaction and integration costs	0	5	0	6
Development activity expenses	5	5	10	12
Total operating costs and expenses	129	153	273	283
Other income - affiliate	42	48	90	96
Gain/(loss) on sale of assets	0	(83)	0	(83)
Operating Income/(Loss)	(87)	(188)	(183)	(270)
Other Income/(Expense)
Equity in earnings/(losses) of consolidated subsidiaries	(123)	67	(48)	342
Equity in (losses)/earnings of unconsolidated affiliates	(645)	7	(669)	10
Gain/(impairment loss) on investment		7		0
Other income	3	2	5	2
Loss on debt extinguishment, net		(76)	0	(65)
Interest expense	(122)	(132)	(239)	(265)
Total other expense	(887)	(125)	(951)	24
Income/(Loss) from Continuing Operations Before Income Taxes	(974)	(313)	(1,134)	(246)
Income tax expense/(benefit)	(376)	(70)	(369)	(87)
Income/(Loss) from Continuing Operations	(598)	(243)	(765)	(159)
Loss from discontinued operations, net of income tax	0	3	0	6
Net Income/(Loss)	(598)	(240)	(765)	(153)
Less: Net (loss)/income attributable to noncontrolling interest and redeemable noncontrolling interests	28	31	25	36
Net Income/(Loss) Attributable to NRG Energy, Inc.	$ (626)	$ (271)	$ (790)	$ (189)