Condensed Consolidating Financial Information - CASH FLOWS (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Cash Flows from Operating Activities
Net income (loss) from continuing operations	$ 99	$ (163)	$ (70)	$ (220)
Adjustments to reconcile net income/(loss) to net cash provided by operating activities:
Distributions from unconsolidated affiliates			28	29
Equity in losses/(earnings) of unconsolidated affiliates			(2)	3
Depreciation and amortization	260	262	517	528
Provision for bad debts			18	20
Amortization of nuclear fuel			24	26
Amortization of financing costs and debt discount/premiums			29	29
Adjustment for debt extinguishment			0	14
Amortization of intangibles and out-of-market contracts			51	82
Amortization of unearned equity compensation			16	16
Impairment losses			63	195
Changes in deferred income taxes and liability for uncertain tax benefits			8	1
Changes in nuclear decommissioning trust liability			2	13
Changes in derivative instruments			7	(7)
Changes in collateral posted in support of risk management activities			(189)	323
Proceeds from sale of emission allowances			11	17
Gain on sale of assets			(22)	83
Cash (used)/provided by changes in other working capital			(379)	(272)
Cash provided by continuing operations			112	880
Cash (used/)provided by discontinued operations			(38)	(69)
Net Cash Provided by Operating Activities			74	811
Cash Flows from Investing Activities
Dividends from NRG Yield, Inc.			0	0
Intercompany dividends			0	0
Acquisition of Drop Down Assets, net of cash acquired			0
Acquisitions of businesses, net of cash acquired			(16)	(17)
Capital expenditures			(542)	(442)
Decrease in notes receivable			8	(3)
Purchases of emission allowances			(30)	(27)
Proceeds from sale of emission allowances			59	25
Investments in nuclear decommissioning trust fund securities			(279)	(280)
Proceeds from the sale of nuclear decommissioning trust fund securities			277	267
Proceeds from renewable energy grants and state rebates			8	10
Proceeds from sale of assets, net of cash disposed of			35	25
Investments in unconsolidated affiliates			(30)	1
Other			18	31
Cash (used)/provided by continuing operations			(492)	(410)
Cash used by discontinued operations			(53)	(60)
Net Cash (Used)/Provided by Investing Activities			(545)	(470)
Cash Flows from Financing Activities
Dividends from NRG Yield, Inc.			0	0
Payments (for)/from intercompany loans			0	0
Acquisition of Drop Down Assets, net of cash acquired			0
Intercompany dividends			0	0
Payment of dividends to common and preferred stockholders			(19)	(57)
Payment for preferred shares			0	(226)
Net receipts from settlement of acquired derivatives that include financing elements			2	4
Proceeds from issuance of long-term debt			946	3,223
Payments for short and long-term debt			(530)	(3,505)
Receivable from affiliate			(125)	0
Contributions to, net of distributions from, noncontrolling interest in subsidiaries			14	(21)
Payment of debt issuance costs			(36)	(35)
Other			(10)	(10)
Cash provided/(used) by continuing operations			242	(627)
Cash used by discontinued operations			(224)	97
Net Cash provided/(used) by Financing Activities			18	(530)
Change in Cash from discontinued operations			(315)	(32)
Effect of exchange rate changes on cash and cash equivalents			(8)	(3)
Net Increase (Decrease) in Cash and Cash Equivalents, Restricted Cash, and Funds Restricted by Counterparties			(146)	(160)
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at Beginning of Period			1,386	1,322
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at End of Period	1,240	1,162	1,240	1,162
Eliminations
Cash Flows from Operating Activities
Net income (loss) from continuing operations	53	(28)	91	(244)
Adjustments to reconcile net income/(loss) to net cash provided by operating activities:
Distributions from unconsolidated affiliates			(4)	(11)
Equity in losses/(earnings) of unconsolidated affiliates			9	4
Depreciation and amortization	0	0	0	0
Provision for bad debts			0	0
Amortization of nuclear fuel			0	0
Amortization of financing costs and debt discount/premiums			0	0
Adjustment for debt extinguishment				0
Amortization of intangibles and out-of-market contracts			0	0
Amortization of unearned equity compensation			0	0
Impairment losses			0	0
Changes in deferred income taxes and liability for uncertain tax benefits			0	0
Changes in nuclear decommissioning trust liability			0	0
Changes in derivative instruments			0	0
Changes in collateral posted in support of risk management activities				0
Proceeds from sale of emission allowances			0	0
Gain on sale of assets			0	0
Cash (used)/provided by changes in other working capital			(96)	251
Cash provided by continuing operations			0	0
Cash (used/)provided by discontinued operations			0
Net Cash Provided by Operating Activities			0	0
Cash Flows from Investing Activities
Dividends from NRG Yield, Inc.			(45)	(39)
Intercompany dividends			(129)	(12)
Acquisition of Drop Down Assets, net of cash acquired			131
Acquisitions of businesses, net of cash acquired			0	0
Capital expenditures			0	0
Decrease in notes receivable			0	0
Purchases of emission allowances			0	0
Proceeds from sale of 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 renewable energy grants and state rebates			0	0
Proceeds from sale of assets, net of cash disposed of			0	0
Investments in unconsolidated affiliates			0	0
Other			0	0
Cash (used)/provided by continuing operations			(43)	(51)
Net Cash (Used)/Provided by Investing Activities			(43)	(51)
Cash Flows from Financing Activities
Dividends from NRG Yield, Inc.			45	39
Payments (for)/from intercompany loans			0	0
Acquisition of Drop Down Assets, net of cash acquired			(131)
Intercompany dividends			129	12
Payment of dividends to common and preferred stockholders			0	0
Payment for preferred shares				0
Net receipts from settlement of acquired derivatives that include financing elements			0	0
Proceeds from issuance of long-term debt			0	0
Payments for short and long-term debt			0	0
Receivable from affiliate			0
Contributions to, net of distributions from, noncontrolling interest in subsidiaries			0	0
Payment of debt issuance costs			0	0
Other			0	0
Cash provided/(used) by continuing operations			43	51
Cash used by discontinued operations			0
Net Cash provided/(used) by Financing Activities			43	51
Change in Cash from discontinued operations			0
Effect of exchange rate changes on cash and cash equivalents			0	0
Net Increase (Decrease) in Cash and Cash Equivalents, Restricted Cash, and Funds Restricted by Counterparties			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 income (loss) from continuing operations	163	204	207	369
Adjustments to reconcile net income/(loss) to net cash provided by operating activities:
Distributions from unconsolidated affiliates			0	0
Equity in losses/(earnings) of unconsolidated affiliates			0	(3)
Depreciation and amortization	102	112	203	225
Provision for bad debts			17	16
Amortization of nuclear fuel			24	26
Amortization of financing costs and debt discount/premiums			0	0
Adjustment for debt extinguishment				0
Amortization of intangibles and out-of-market contracts			12	20
Amortization of unearned equity compensation			0	0
Impairment losses			42	0
Changes in deferred income taxes and liability for uncertain tax benefits			131	460
Changes in nuclear decommissioning trust liability			2	13
Changes in derivative instruments			12	(64)
Changes in collateral posted in support of risk management activities			(203)	344
Proceeds from sale of emission allowances			11	47
Gain on sale of assets			(22)	0
Cash (used)/provided by changes in other working capital			(298)	(1,148)
Cash provided by continuing operations			138	305
Cash (used/)provided by discontinued operations			0
Net Cash Provided by Operating Activities			138	305
Cash Flows from Investing Activities
Dividends from NRG Yield, Inc.				0
Intercompany dividends			0	0
Acquisition of Drop Down Assets, net of cash acquired			0
Acquisitions of businesses, net of cash acquired				0
Capital expenditures			(90)	(80)
Decrease in notes receivable			0	0
Purchases of emission allowances			(30)	(27)
Proceeds from sale of emission allowances			59	25
Investments in nuclear decommissioning trust fund securities			(279)	(280)
Proceeds from the sale of nuclear decommissioning trust fund securities			277	267
Proceeds from renewable energy grants and state rebates			8	0
Proceeds from sale of assets, net of cash disposed of			35	0
Investments in unconsolidated affiliates			0	1
Other			18	27
Cash (used)/provided by continuing operations			(2)	(67)
Net Cash (Used)/Provided by Investing Activities			(2)	(67)
Cash Flows from Financing Activities
Dividends from NRG Yield, Inc.			0	0
Payments (for)/from intercompany loans			(122)	(179)
Acquisition of Drop Down Assets, net of cash acquired			0
Intercompany dividends				(52)
Payment of dividends to common and preferred stockholders			0	0
Payment for preferred shares				0
Net receipts from settlement of acquired derivatives that include financing elements			0	0
Proceeds from issuance of long-term debt			0	0
Payments for short and long-term debt			0	(1)
Receivable from affiliate			0
Contributions to, net of distributions from, noncontrolling interest in subsidiaries			0	0
Payment of debt issuance costs			0	0
Other				(3)
Cash provided/(used) by continuing operations			(122)	(235)
Cash used by discontinued operations			0
Net Cash provided/(used) by Financing Activities			(122)	(235)
Change in Cash from discontinued operations			0
Effect of exchange rate changes on cash and cash equivalents			0	0
Net Increase (Decrease) in Cash and Cash Equivalents, Restricted Cash, and Funds Restricted by Counterparties			14	3
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at Beginning of Period			4	0
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at End of Period	18	3	18	3
Non-Guarantor Subsidiaries
Cash Flows from Operating Activities
Net income (loss) from continuing operations	481	(96)	397	(186)
Adjustments to reconcile net income/(loss) to net cash provided by operating activities:
Distributions from unconsolidated affiliates			32	40
Equity in losses/(earnings) of unconsolidated affiliates			(13)	2
Depreciation and amortization	150	144	298	291
Provision for bad debts			1	4
Amortization of nuclear fuel			0	0
Amortization of financing costs and debt discount/premiums			20	16
Adjustment for debt extinguishment				4
Amortization of intangibles and out-of-market contracts			39	62
Amortization of unearned equity compensation			0	0
Impairment losses			21	195
Changes in deferred income taxes and liability for uncertain tax benefits			237	(208)
Changes in nuclear decommissioning trust liability			0	0
Changes in derivative instruments			(12)	54
Changes in collateral posted in support of risk management activities			11	(21)
Proceeds from sale of emission allowances			0	(30)
Gain on sale of assets			0	8
Cash (used)/provided by changes in other working capital			(1,138)	239
Cash provided by continuing operations			(107)	470
Cash (used/)provided by discontinued operations			(38)	(69)
Net Cash Provided by Operating Activities			(145)	401
Cash Flows from Investing Activities
Dividends from NRG Yield, Inc.				0
Intercompany dividends			0	0
Acquisition of Drop Down Assets, net of cash acquired			(131)
Acquisitions of businesses, net of cash acquired			(16)	(17)
Capital expenditures			(436)	(329)
Decrease in notes receivable			8	(3)
Purchases of emission allowances			0	0
Proceeds from sale of 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 renewable energy grants and state rebates			0	10
Proceeds from sale of assets, net of cash disposed of			0	0
Investments in unconsolidated affiliates			(30)	0
Other			0	4
Cash (used)/provided by continuing operations			(605)	(335)
Cash used by discontinued operations			(53)	(60)
Net Cash (Used)/Provided by Investing Activities			(658)	(395)
Cash Flows from Financing Activities
Dividends from NRG Yield, Inc.			(45)	(39)
Payments (for)/from intercompany loans			369	45
Acquisition of Drop Down Assets, net of cash acquired			0
Intercompany dividends			(129)	40
Payment of dividends to common and preferred stockholders			0	0
Payment for preferred shares				0
Net receipts from settlement of acquired derivatives that include financing elements			2	4
Proceeds from issuance of long-term debt			741	332
Payments for short and long-term debt			(316)	(279)
Receivable from affiliate			(125)
Contributions to, net of distributions from, noncontrolling interest in subsidiaries			14	(21)
Payment of debt issuance costs			(32)	0
Other			(10)	(7)
Cash provided/(used) by continuing operations			469	75
Cash used by discontinued operations			(224)	97
Net Cash provided/(used) by Financing Activities			245	172
Change in Cash from discontinued operations			(315)	(32)
Effect of exchange rate changes on cash and cash equivalents			(8)	(3)
Net Increase (Decrease) in Cash and Cash Equivalents, Restricted Cash, and Funds Restricted by Counterparties			(251)	207
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at Beginning of Period			1,059	629
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at End of Period	808	836	808	836
NRG Energy, Inc. (Note Issuer)
Cash Flows from Operating Activities
Net income (loss) from continuing operations	(598)	(243)	(765)	(159)
Adjustments to reconcile net income/(loss) to net cash provided by operating activities:
Distributions from unconsolidated affiliates			0	0
Equity in losses/(earnings) of unconsolidated affiliates			2	0
Depreciation and amortization	8	6	16	12
Provision for bad debts			0	0
Amortization of nuclear fuel			0	0
Amortization of financing costs and debt discount/premiums			9	13
Adjustment for debt extinguishment				10
Amortization of intangibles and out-of-market contracts			0	0
Amortization of unearned equity compensation			16	16
Impairment losses			0	0
Changes in deferred income taxes and liability for uncertain tax benefits			(360)	(251)
Changes in nuclear decommissioning trust liability			0	0
Changes in derivative instruments			7	3
Changes in collateral posted in support of risk management activities			3	0
Proceeds from sale of emission allowances			0	0
Gain on sale of assets			0	75
Cash (used)/provided by changes in other working capital			1,153	386
Cash provided by continuing operations			81	105
Cash (used/)provided by discontinued operations			0
Net Cash Provided by Operating Activities			81	105
Cash Flows from Investing Activities
Dividends from NRG Yield, Inc.			45	39
Intercompany dividends			129	12
Acquisition of Drop Down Assets, net of cash acquired			0
Acquisitions of businesses, net of cash acquired			0	0
Capital expenditures			(16)	(33)
Decrease in notes receivable			0	0
Purchases of emission allowances				0
Proceeds from sale of 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 renewable energy grants and state rebates			0	0
Proceeds from sale of assets, net of cash disposed of			0	25
Investments in unconsolidated affiliates			0	0
Other				0
Cash (used)/provided by continuing operations			158	43
Net Cash (Used)/Provided by Investing Activities			158	43
Cash Flows from Financing Activities
Dividends from NRG Yield, Inc.			0	0
Payments (for)/from intercompany loans			(247)	134
Acquisition of Drop Down Assets, net of cash acquired			131
Intercompany dividends				0
Payment of dividends to common and preferred stockholders			(19)	(57)
Payment for preferred shares				(226)
Net receipts from settlement of acquired derivatives that include financing elements			0	0
Proceeds from issuance of long-term debt			205	2,891
Payments for short and long-term debt			(214)	(3,225)
Receivable from affiliate			0
Contributions to, net of distributions from, noncontrolling interest in subsidiaries			0	0
Payment of debt issuance costs			(4)	(35)
Other				0
Cash provided/(used) by continuing operations			(148)	(518)
Cash used by discontinued operations			0
Net Cash provided/(used) by Financing Activities			(148)	(518)
Change in Cash from discontinued operations			0
Effect of exchange rate changes on cash and cash equivalents			0	0
Net Increase (Decrease) in Cash and Cash Equivalents, Restricted Cash, and Funds Restricted by Counterparties			91	(370)
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at Beginning of Period			323	693
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at End of Period	$ 414	$ 323	$ 414	$ 323