Segment Reporting (Details) - USD ($) $ in Millions		12 Months Ended
	Aug. 24, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Jan. 05, 2021
Income Statement
Revenues		$ 26,989	$ 9,093	$ 9,821
Operating expenses		22,566	7,481	8,160
Depreciation and amortization		785	435	373
Impairment losses		544	75	5
Total operating cost and expenses		23,895	7,991	8,538
Gain on sale of assets		247	3	7
Operating income		3,341	1,105	1,290
Equity in (losses)/earnings of unconsolidated affiliates		17	17	2
Impairment losses on investments		0	(18)	(108)
Other income, net		63	67	66
Loss on debt extinguishment	$ 77	(77)	(9)	(51)
Interest expense		(485)	(401)	(413)
Income from Continuing Operations Before Income Taxes		2,859	761	786
Income tax expense/(benefit)		672	251	(3,334)
Income from Continuing Operations		2,187	510	4,120
Income from discontinued operations, net of income tax		0	0	321
Net Income		2,187	510	4,441
Less: Net income attributable to noncontrolling interests and redeemable noncontrolling interests		0	0	3
Net Income Attributable to NRG Energy, Inc.		2,187	510	4,438
Balance sheet
Equity investments in affiliates		157	346
Capital expenditures		269	230
Goodwill		1,795	579
Total assets		23,182	14,902
Corporate
Income Statement
Revenues		0	0	0
Operating expenses		141	57	50
Depreciation and amortization		28	34	31
Impairment losses		0	0	0
Total operating cost and expenses		169	91	81
Gain on sale of assets		211	5	6
Operating income		42	(86)	(75)
Equity in (losses)/earnings of unconsolidated affiliates		0	0	0
Impairment losses on investments			0	(5)
Other income, net		59	41	30
Loss on debt extinguishment		(77)	0	(48)
Interest expense		(469)	(384)	(385)
Income from Continuing Operations Before Income Taxes		(445)	(429)	(483)
Income tax expense/(benefit)		653	250	(3,337)
Income from Continuing Operations				2,854
Income from discontinued operations, net of income tax				321
Net Income				3,175
Less: Net income attributable to noncontrolling interests and redeemable noncontrolling interests				0
Net Income Attributable to NRG Energy, Inc.		(1,098)	(679)	3,175
Balance sheet
Equity investments in affiliates		0	0
Capital expenditures		45	25
Goodwill		0	0
Total assets		19,081	11,152
Eliminations
Income Statement
Revenues		10	(4)	(7)
Operating expenses		10	(4)	(7)
Depreciation and amortization		0	0	0
Impairment losses		0	0	0
Total operating cost and expenses		10	(4)	(7)
Gain on sale of assets		0	0	0
Operating income		0	0	0
Equity in (losses)/earnings of unconsolidated affiliates		0	0	0
Impairment losses on investments			0	0
Other income, net		(14)	0	0
Loss on debt extinguishment		0	0	0
Interest expense		14	0	0
Income from Continuing Operations Before Income Taxes		0	0	0
Income tax expense/(benefit)		0	0	0
Income from Continuing Operations				0
Income from discontinued operations, net of income tax				0
Net Income				0
Less: Net income attributable to noncontrolling interests and redeemable noncontrolling interests				0
Net Income Attributable to NRG Energy, Inc.		0	0	0
Balance sheet
Equity investments in affiliates		0	0
Capital expenditures		0	0
Goodwill		0	0
Total assets		(26,653)	(7,360)
Texas
Balance sheet
Goodwill		751	324		$ 427
Texas | Operating Segments
Income Statement
Revenues		10,293	6,309	7,069
Operating expenses		8,692	5,249	5,821
Depreciation and amortization		331	227	188
Impairment losses		0	14	1
Total operating cost and expenses		9,023	5,490	6,010
Gain on sale of assets		19	0	0
Operating income		1,289	819	1,059
Equity in (losses)/earnings of unconsolidated affiliates		(3)	(12)	(4)
Impairment losses on investments			(18)	(103)
Other income, net		8	11	20
Loss on debt extinguishment		0	0	0
Interest expense		(1)	0	0
Income from Continuing Operations Before Income Taxes		1,293	800	972
Income tax expense/(benefit)		0	0	0
Income from Continuing Operations				972
Income from discontinued operations, net of income tax				0
Net Income				972
Less: Net income attributable to noncontrolling interests and redeemable noncontrolling interests				0
Net Income Attributable to NRG Energy, Inc.		1,293	800	972
Balance sheet
Equity investments in affiliates		0	(13)
Capital expenditures		153	130
Goodwill		751	324
Total assets		12,265	7,641
Texas | Eliminations
Income Statement
Revenues		(5)	(6)	(1)
East
Balance sheet
Goodwill		853	240		$ 648
East | Operating Segments
Income Statement
Revenues		13,033	2,258	2,262
Operating expenses		10,257	1,758	1,843
Depreciation and amortization		338	138	117
Impairment losses		535	0	0
Total operating cost and expenses		11,130	1,896	1,960
Gain on sale of assets		0	0	1
Operating income		1,903	362	303
Equity in (losses)/earnings of unconsolidated affiliates		0	0	0
Impairment losses on investments			0	0
Other income, net		7	7	6
Loss on debt extinguishment		0	(4)	0
Interest expense		(1)	(14)	(18)
Income from Continuing Operations Before Income Taxes		1,909	351	291
Income tax expense/(benefit)		0	(1)	2
Income from Continuing Operations				289
Income from discontinued operations, net of income tax				0
Net Income				289
Less: Net income attributable to noncontrolling interests and redeemable noncontrolling interests				0
Net Income Attributable to NRG Energy, Inc.		1,909	352	289
Balance sheet
Equity investments in affiliates		0	0
Capital expenditures		50	45
Goodwill		853	240
Total assets		13,673	1,790
East | Eliminations
Income Statement
Revenues		18	6	(8)
West/Services/Other
Balance sheet
Goodwill		191	15
West/Services/Other | Operating Segments
Income Statement
Revenues		3,653	530	497
Operating expenses		3,466	421	453
Depreciation and amortization		88	36	37
Impairment losses		9	61	4
Total operating cost and expenses		3,563	518	494
Gain on sale of assets		17	(2)	0
Operating income		107	10	3
Equity in (losses)/earnings of unconsolidated affiliates		20	29	6
Impairment losses on investments			0	0
Other income, net		3	8	10
Loss on debt extinguishment		0	(5)	(3)
Interest expense		(28)	(3)	(10)
Income from Continuing Operations Before Income Taxes		102	39	6
Income tax expense/(benefit)		19	2	1
Income from Continuing Operations				5
Income from discontinued operations, net of income tax				0
Net Income				5
Less: Net income attributable to noncontrolling interests and redeemable noncontrolling interests				3
Net Income Attributable to NRG Energy, Inc.		83	37	2
Balance sheet
Equity investments in affiliates		157	359
Capital expenditures		21	30
Goodwill		191	15
Total assets		4,816	1,679
West/Services/Other | Eliminations
Income Statement
Revenues		$ (3)	$ (4)	$ 2