Condensed Consolidating Financial Information - CONSOLIDATING STATEMENTS OF CASH FLOWS (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Cash Flows from Operating Activities
Net (loss)/income	$ 202	$ 96	$ 684	$ 329
Income/(loss) from discontinued operations	13	69	401	64
Income/(loss) from continuing operations	189	27	283	265
Adjustments to reconcile net income to net cash provided/(used) by operating activities:
Distributions and equity in (earnings)/losses of unconsolidated affiliates and consolidated subsidiaries			22	12
Depreciation, amortization and accretion			184	252
Provision for bad debts			52	30
Amortization of nuclear fuel			27	24
Amortization of financing costs and debt discount/premiums			13	13
Loss on debt extinguishment, net			47	3
Amortization of intangibles and out-of-market contracts			14	20
Amortization of unearned equity compensation			10	15
(Loss)/gain on sale and disposal of assets			1	(16)
Impairment losses			1	88
Changes in derivative instruments			(22)	(145)
Changes in deferred income taxes and liability for uncertain tax benefits			(5)	(2)
Changes in collateral deposits in support of energy risk management activities			125	(9)
Changes in nuclear decommissioning trust liability			17	41
Loss on deconsolidation of Ivanpah project			0	22
Changes in other working capital			(388)	(349)
Cash provided/(used) by continuing operations			381	264
Cash provided/(used) by discontinued operations			8	249
Net Cash Provided/(Used) by Operating Activities			389	513
Cash Flows from Investing Activities
Intercompany dividends			0	0
Payments for acquisitions of businesses			(21)	(211)
Capital expenditures			(107)	(282)
Net purchases of /proceeds from emission allowances			(1)	3
Investments in nuclear decommissioning trust fund securities			(209)	(346)
Proceeds from the sale of nuclear decommissioning trust fund securities			191	303
Proceeds from sale of assets, net of cash disposed and sale of discontinued operations, net of fees			1,289	146
Deconsolidation of Ivanpah project			0	(160)
Net contributions for investments in unconsolidated affiliates			7	(15)
Contributions to discontinued operations			(44)	(16)
Cash (used)/provided by continuing operations			1,105	(578)
Cash used by discontinued operations			(2)	(584)
Net Cash (Used)/Provided by Investing Activities			1,103	(1,162)
Cash Flows from Financing Activities
Payments from/(for) intercompany loans			0	0
Intercompany dividends			0	0
Payments of dividends to common stockholders			(16)	(19)
Payments for treasury stock			(1,039)	(500)
Payments for debt extinguishment			(24)	0
Distributions to noncontrolling interests from subsidiaries			(1)	(14)
Proceeds from issuance of common stock			2	11
Proceeds from issuance of long-term debt			1,833
Proceeds from issuance of short and long-term debt			1,833	994
Payment of debt issuance costs			(33)	(19)
Payments for short and long-term debt			(2,485)	(348)
Cash (used)/provided by continuing operations			(1,763)	105
Cash provided by discontinued operations			43	345
Net Cash (Used)/Provided by Financing Activities			(1,720)	450
Change in cash from discontinued operations			49	10
Net Decrease in Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash			(277)	(209)
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at Beginning of Period			613	1,086
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at End of Period	336	877	336	877
Eliminations
Cash Flows from Operating Activities
Net (loss)/income	(432)	(358)	(741)	(691)
Income/(loss) from discontinued operations	0	0	0	0
Income/(loss) from continuing operations	(432)	(358)	(741)	(691)
Adjustments to reconcile net income to net cash provided/(used) by operating activities:
Distributions and equity in (earnings)/losses of unconsolidated affiliates and consolidated subsidiaries			741	691
Depreciation, amortization and accretion			0	0
Provision for bad debts			0	0
Amortization of nuclear fuel			0	0
Amortization of financing costs and debt discount/premiums			0	0
Loss on debt extinguishment, net			0	0
Amortization of intangibles and out-of-market contracts			0	0
Amortization of unearned equity compensation			0	0
(Loss)/gain on sale and disposal of assets			0	0
Impairment losses			0	0
Changes in derivative instruments			0	0
Changes in deferred income taxes and liability for uncertain tax benefits			0	0
Changes in collateral deposits in support of energy risk management activities			0	0
Changes in nuclear decommissioning trust liability			0	0
Loss on deconsolidation of Ivanpah project				0
Changes in other working capital			0	0
Cash provided/(used) by continuing operations			0	0
Cash provided/(used) by discontinued operations			0	0
Net Cash Provided/(Used) by Operating Activities			0	0
Cash Flows from Investing Activities
Intercompany dividends			(738)	(157)
Payments for acquisitions of businesses			0	0
Capital expenditures			0	0
Net purchases of /proceeds from emission allowances			0	0
Investments in nuclear decommissioning trust fund securities			0	0
Proceeds from the sale of nuclear decommissioning trust fund securities			0	0
Proceeds from sale of assets, net of cash disposed and sale of discontinued operations, net of fees				0
Deconsolidation of Ivanpah project				0
Net contributions for investments in unconsolidated affiliates			0	0
Contributions to discontinued operations			0	0
Cash (used)/provided by continuing operations			(738)	(157)
Cash used by discontinued operations			0	0
Net Cash (Used)/Provided by Investing Activities			(738)	(157)
Cash Flows from Financing Activities
Payments from/(for) intercompany loans			0	0
Intercompany dividends			738	157
Payments of dividends to common stockholders			0	0
Payments for treasury stock			0	0
Payments for debt extinguishment			0
Distributions to noncontrolling interests from subsidiaries			0	0
Proceeds from issuance of common stock			0	0
Proceeds from issuance of long-term debt			0
Proceeds from issuance of short and long-term debt				0
Payment of debt issuance costs			0	0
Payments for short and long-term debt			0	0
Cash (used)/provided by continuing operations			738	157
Cash provided by discontinued operations			0	0
Net Cash (Used)/Provided by Financing Activities			738	157
Change in cash from discontinued operations			0	0
Net Decrease in Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash			0	0
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at Beginning of Period			0	0
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at End of Period	0	0	0	0
Guarantor Subsidiaries
Cash Flows from Operating Activities
Net (loss)/income	389	211	644	542
Income/(loss) from discontinued operations	0	15	9	30
Income/(loss) from continuing operations	389	196	635	512
Adjustments to reconcile net income to net cash provided/(used) by operating activities:
Distributions and equity in (earnings)/losses of unconsolidated affiliates and consolidated subsidiaries			(12)	(8)
Depreciation, amortization and accretion			115	136
Provision for bad debts			42	30
Amortization of nuclear fuel			27	24
Amortization of financing costs and debt discount/premiums			0	0
Loss on debt extinguishment, net			0	0
Amortization of intangibles and out-of-market contracts			13	16
Amortization of unearned equity compensation			0	0
(Loss)/gain on sale and disposal of assets			(3)	(3)
Impairment losses			1	0
Changes in derivative instruments			(28)	(154)
Changes in deferred income taxes and liability for uncertain tax benefits			0	221
Changes in collateral deposits in support of energy risk management activities			128	(5)
Changes in nuclear decommissioning trust liability			17	41
Loss on deconsolidation of Ivanpah project				0
Changes in other working capital			(343)	152
Cash provided/(used) by continuing operations			592	962
Cash provided/(used) by discontinued operations			17	50
Net Cash Provided/(Used) by Operating Activities			609	1,012
Cash Flows from Investing Activities
Intercompany dividends			0	0
Payments for acquisitions of businesses			(21)	(2)
Capital expenditures			(77)	(103)
Net purchases of /proceeds from emission allowances			(1)	3
Investments in nuclear decommissioning trust fund securities			(209)	(346)
Proceeds from the sale of nuclear decommissioning trust fund securities			191	303
Proceeds from sale of assets, net of cash disposed and sale of discontinued operations, net of fees			1	11
Deconsolidation of Ivanpah project				0
Net contributions for investments in unconsolidated affiliates			0	0
Contributions to discontinued operations			0	0
Cash (used)/provided by continuing operations			(116)	(134)
Cash used by discontinued operations			0	2
Net Cash (Used)/Provided by Investing Activities			(116)	(132)
Cash Flows from Financing Activities
Payments from/(for) intercompany loans			206	(611)
Intercompany dividends			(738)	(157)
Payments of dividends to common stockholders			0	0
Payments for treasury stock			0	0
Payments for debt extinguishment			0
Distributions to noncontrolling interests from subsidiaries			0	0
Proceeds from issuance of common stock			0	0
Proceeds from issuance of long-term debt			0
Proceeds from issuance of short and long-term debt				0
Payment of debt issuance costs			0	0
Payments for short and long-term debt			0	0
Cash (used)/provided by continuing operations			(532)	(768)
Cash provided by discontinued operations			0	0
Net Cash (Used)/Provided by Financing Activities			(532)	(768)
Change in cash from discontinued operations			17	52
Net Decrease in Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash			(56)	60
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at Beginning of Period			95	41
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at End of Period	39	101	39	101
Non-Guarantor Subsidiaries
Cash Flows from Operating Activities
Net (loss)/income	44	93	98	32
Income/(loss) from discontinued operations	0	80	5	60
Income/(loss) from continuing operations	44	13	93	(28)
Adjustments to reconcile net income to net cash provided/(used) by operating activities:
Distributions and equity in (earnings)/losses of unconsolidated affiliates and consolidated subsidiaries			22	11
Depreciation, amortization and accretion			53	99
Provision for bad debts			4	0
Amortization of nuclear fuel			0	0
Amortization of financing costs and debt discount/premiums			0	1
Loss on debt extinguishment, net			0	0
Amortization of intangibles and out-of-market contracts			1	4
Amortization of unearned equity compensation			0	0
(Loss)/gain on sale and disposal of assets			1	(13)
Impairment losses			0	88
Changes in derivative instruments			(32)	19
Changes in deferred income taxes and liability for uncertain tax benefits			(3)	(47)
Changes in collateral deposits in support of energy risk management activities			(3)	(4)
Changes in nuclear decommissioning trust liability			0	0
Loss on deconsolidation of Ivanpah project				22
Changes in other working capital			(64)	(56)
Cash provided/(used) by continuing operations			72	96
Cash provided/(used) by discontinued operations			(9)	199
Net Cash Provided/(Used) by Operating Activities			63	295
Cash Flows from Investing Activities
Intercompany dividends			0	0
Payments for acquisitions of businesses			0	(209)
Capital expenditures			(15)	(149)
Net purchases of /proceeds from emission allowances			0	0
Investments in nuclear decommissioning trust fund securities			0	0
Proceeds from the sale of nuclear decommissioning trust fund securities			0	0
Proceeds from sale of assets, net of cash disposed and sale of discontinued operations, net of fees			400	0
Deconsolidation of Ivanpah project				(160)
Net contributions for investments in unconsolidated affiliates			7	(15)
Contributions to discontinued operations			(44)	(16)
Cash (used)/provided by continuing operations			348	(549)
Cash used by discontinued operations			(2)	(586)
Net Cash (Used)/Provided by Investing Activities			346	(1,135)
Cash Flows from Financing Activities
Payments from/(for) intercompany loans			(375)	204
Intercompany dividends			0	0
Payments of dividends to common stockholders			0	0
Payments for treasury stock			0	0
Payments for debt extinguishment			0
Distributions to noncontrolling interests from subsidiaries			(1)	(14)
Proceeds from issuance of common stock			0	0
Proceeds from issuance of long-term debt			0
Proceeds from issuance of short and long-term debt				163
Payment of debt issuance costs			0	0
Payments for short and long-term debt			(53)	(63)
Cash (used)/provided by continuing operations			(429)	290
Cash provided by discontinued operations			43	345
Net Cash (Used)/Provided by Financing Activities			(386)	635
Change in cash from discontinued operations			32	(42)
Net Decrease in Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash			(9)	(163)
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at Beginning of Period			38	425
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at End of Period	29	262	29	262
NRG Energy, Inc. (Note Issuer)
Cash Flows from Operating Activities
Net (loss)/income	201	150	683	446
Income/(loss) from discontinued operations	13	(26)	387	(26)
Income/(loss) from continuing operations	188	176	296	472
Adjustments to reconcile net income to net cash provided/(used) by operating activities:
Distributions and equity in (earnings)/losses of unconsolidated affiliates and consolidated subsidiaries			(729)	(682)
Depreciation, amortization and accretion			16	17
Provision for bad debts			6	0
Amortization of nuclear fuel			0	0
Amortization of financing costs and debt discount/premiums			13	12
Loss on debt extinguishment, net			47	3
Amortization of intangibles and out-of-market contracts			0	0
Amortization of unearned equity compensation			10	15
(Loss)/gain on sale and disposal of assets			3	0
Impairment losses			0	0
Changes in derivative instruments			38	(10)
Changes in deferred income taxes and liability for uncertain tax benefits			(2)	(176)
Changes in collateral deposits in support of energy risk management activities			0	0
Changes in nuclear decommissioning trust liability			0	0
Loss on deconsolidation of Ivanpah project				0
Changes in other working capital			19	(445)
Cash provided/(used) by continuing operations			(283)	(794)
Cash provided/(used) by discontinued operations			0	0
Net Cash Provided/(Used) by Operating Activities			(283)	(794)
Cash Flows from Investing Activities
Intercompany dividends			738	157
Payments for acquisitions of businesses			0	0
Capital expenditures			(15)	(30)
Net purchases of /proceeds from emission allowances			0	0
Investments in nuclear decommissioning trust fund securities			0	0
Proceeds from the sale of nuclear decommissioning trust fund securities			0	0
Proceeds from sale of assets, net of cash disposed and sale of discontinued operations, net of fees			888	135
Deconsolidation of Ivanpah project				0
Net contributions for investments in unconsolidated affiliates			0	0
Contributions to discontinued operations			0	0
Cash (used)/provided by continuing operations			1,611	262
Cash used by discontinued operations			0	0
Net Cash (Used)/Provided by Investing Activities			1,611	262
Cash Flows from Financing Activities
Payments from/(for) intercompany loans			169	407
Intercompany dividends			0	0
Payments of dividends to common stockholders			(16)	(19)
Payments for treasury stock			(1,039)	(500)
Payments for debt extinguishment			(24)
Distributions to noncontrolling interests from subsidiaries			0	0
Proceeds from issuance of common stock			2	11
Proceeds from issuance of long-term debt			1,833
Proceeds from issuance of short and long-term debt				831
Payment of debt issuance costs			(33)	(19)
Payments for short and long-term debt			(2,432)	(285)
Cash (used)/provided by continuing operations			(1,540)	426
Cash provided by discontinued operations			0	0
Net Cash (Used)/Provided by Financing Activities			(1,540)	426
Change in cash from discontinued operations			0	0
Net Decrease in Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash			(212)	(106)
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at Beginning of Period			480	620
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at End of Period	$ 268	$ 514	$ 268	$ 514