The aggregate (income) expense recorded in earnings to allocate the cost of out-of-market contracts and intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash (income) expense, this element is added back to net income when calculating cash provided by (used in) operations using the indirect method.

No definition available.

Condensed Consolidating Financial Information - CONSOLIDATING STATEMENTS OF CASH FLOWS (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Cash Flows from Operating Activities
Net income attributable to NRG Energy, Inc.	$ 249	$ 313	$ 121	$ 372	$ 201	$ 482	$ 683	$ 1,055
Net Income	249			372			683	1,056
Income from discontinued operations	0			(2)			0	399
Income from continuing operations	249			374			683	657
Adjustments to reconcile net income/(loss) to cash provided by operating activities:
Distributions from and equity in losses/(earnings) of unconsolidated affiliates							6	(5)
Depreciation and amortization							318	261
Accretion of asset retirement obligations							46	31
Provision for credit losses	26						74	87
Amortization of nuclear fuel							40	40
Amortization of financing costs and debt discount/premiums							23	20
Loss on debt extinguishment, net							1	47
Amortization of emissions allowances and energy credits							60	28
Amortization of unearned equity compensation							17	15
Net loss on sale of assets and disposal of assets							(22)	(20)
Impairment losses							47	108
Changes in derivative instruments							(7)	36
Changes in deferred income taxes and liability for uncertain tax benefits							202	(3)
Changes in collateral deposits in support of energy risk management activities							96	129
Changes in nuclear decommissioning trust liability							39	27
Changes in other working capital							(237)	(569)
Cash provided/(used) by continuing operations							1,386	889
Cash provided/(used) by discontinued operations							0	8
Net Cash Provided/(Used) by Operating Activities							1,386	897
Cash Flows from Investing Activities
Intercompany dividends							0	0
Payments for acquisitions of businesses							(277)	(348)
Capital expenditures							(167)	(183)
Decrease in notes receivable							0	2
Net purchases of /proceeds from emission allowances							(15)	14
Investments in nuclear decommissioning trust fund securities							(360)	(295)
Proceeds from the sale of nuclear decommissioning trust fund securities							318	271
Proceeds from sale of assets, net of cash disposed and sale of discontinued operations, net of fees							15	1,293
Net distributions from investments in unconsolidated affiliates							2	(94)
Contributions to discontinued operations							0	(44)
Cash (used)/provided by continuing operations							(484)	616
Cash used by discontinued operations							0	(2)
Net Cash (Used)/Provided by Investing Activities							(484)	614
Cash Flows from Financing Activities
Intercompany dividends and transfers							0	0
Payments of dividends to common stockholders							(221)	(24)
Payments for share repurchase activity							(229)	(1,322)
Payments for debt extinguishment costs							0	(24)
Purchase of and distributions to noncontrolling interests from subsidiaries							(2)	(1)
Proceeds from issuance of common stock							1	3
Proceeds from issuance of long-term debt							59	1,833
Payments of debt issuance costs							(24)	(34)
Repayments of long-term debt							(62)	(2,487)
Net (repayments)/proceeds of Revolving Credit Facility							(83)	215
Other							(6)	0
Cash used by continuing operations							(567)	(1,841)
Cash provided by discontinued operations							0	43
Net Cash Used by Financing Activities							(567)	(1,798)
Effect of exchange rate changes on cash and cash equivalents							(2)	0
Change in Cash from discontinued operations							0	49
Net Increase/(Decrease) in Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash							333	(336)
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at Beginning of Period			385			613	385	613
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at End of Period	718			277			718	277
Eliminations
Cash Flows from Operating Activities
Net income attributable to NRG Energy, Inc.	(540)			(557)			(1,391)	(1,298)
Net Income	(540)			(557)			(1,391)	(1,298)
Income from discontinued operations				0				0
Income from continuing operations				(557)				(1,298)
Adjustments to reconcile net income/(loss) to cash provided by operating activities:
Distributions from and equity in losses/(earnings) of unconsolidated affiliates							1,391	1,298
Depreciation and amortization							0	0
Accretion of asset retirement obligations							0	0
Provision for credit losses							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 emissions allowances and energy credits							0	0
Amortization of unearned equity compensation							0	0
Net loss on sale of assets 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
Changes in other working capital							0	0
Cash provided/(used) by continuing operations								0
Cash provided/(used) by discontinued operations								0
Net Cash Provided/(Used) by Operating Activities							0	0
Cash Flows from Investing Activities
Intercompany dividends							(2,591)	(3,866)
Payments for acquisitions of businesses							0	0
Capital expenditures							0	0
Decrease in notes receivable								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	0
Net distributions from investments in unconsolidated affiliates							0	0
Contributions to discontinued operations								0
Cash (used)/provided by continuing operations								(3,866)
Cash used by discontinued operations								0
Net Cash (Used)/Provided by Investing Activities							(2,591)	(3,866)
Cash Flows from Financing Activities
Intercompany dividends and transfers							2,591	3,866
Payments of dividends to common stockholders							0	0
Payments for share repurchase activity							0	0
Payments for debt extinguishment costs								0
Purchase of and distributions to noncontrolling interests from subsidiaries							0	0
Proceeds from issuance of common stock							0	0
Proceeds from issuance of long-term debt							0	0
Payments of debt issuance costs							0	0
Repayments of long-term debt							0	0
Net (repayments)/proceeds of Revolving Credit Facility							0	0
Other							0
Cash used by continuing operations								3,866
Cash provided by discontinued operations								0
Net Cash Used by Financing Activities							2,591	3,866
Effect of exchange rate changes on cash and cash equivalents							0
Change in Cash from discontinued operations								0
Net Increase/(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	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 attributable to NRG Energy, Inc.	492			588			1,334	1,232
Net Income	492			588			1,334	1,232
Income from discontinued operations				0				9
Income from continuing operations				588				1,223
Adjustments to reconcile net income/(loss) to cash provided by operating activities:
Distributions from and equity in losses/(earnings) of unconsolidated affiliates							(6)	(32)
Depreciation and amortization							232	156
Accretion of asset retirement obligations							19	25
Provision for credit losses							66	72
Amortization of nuclear fuel							40	40
Amortization of financing costs and debt discount/premiums							0	0
Loss on debt extinguishment, net							0	0
Amortization of emissions allowances and energy credits							46	21
Amortization of unearned equity compensation							0	0
Net loss on sale of assets and disposal of assets							(16)	(25)
Impairment losses							0	1
Changes in derivative instruments							(27)	10
Changes in deferred income taxes and liability for uncertain tax benefits							(52)	0
Changes in collateral deposits in support of energy risk management activities							91	136
Changes in nuclear decommissioning trust liability							39	27
Changes in other working capital							355	(401)
Cash provided/(used) by continuing operations								1,253
Cash provided/(used) by discontinued operations								17
Net Cash Provided/(Used) by Operating Activities							2,121	1,270
Cash Flows from Investing Activities
Intercompany dividends							0	0
Payments for acquisitions of businesses							(15)	(348)
Capital expenditures							(115)	(135)
Decrease in notes receivable								0
Net purchases of /proceeds from emission allowances							(15)	14
Investments in nuclear decommissioning trust fund securities							(360)	(295)
Proceeds from the sale of nuclear decommissioning trust fund securities							318	271
Proceeds from sale of assets, net of cash disposed and sale of discontinued operations, net of fees							8	1
Net distributions from investments in unconsolidated affiliates							0	0
Contributions to discontinued operations								0
Cash (used)/provided by continuing operations								(492)
Cash used by discontinued operations								0
Net Cash (Used)/Provided by Investing Activities							(179)	(492)
Cash Flows from Financing Activities
Intercompany dividends and transfers							(1,894)	(824)
Payments of dividends to common stockholders							0	0
Payments for share repurchase activity							0	0
Payments for debt extinguishment costs								0
Purchase of and distributions to noncontrolling interests from subsidiaries							0	0
Proceeds from issuance of common stock							0	0
Proceeds from issuance of long-term debt							0	0
Payments of debt issuance costs							0	0
Repayments of long-term debt							(59)	0
Net (repayments)/proceeds of Revolving Credit Facility							0	0
Other							(6)
Cash used by continuing operations								(824)
Cash provided by discontinued operations								0
Net Cash Used by Financing Activities							(1,959)	(824)
Effect of exchange rate changes on cash and cash equivalents							0
Change in Cash from discontinued operations								17
Net Increase/(Decrease) in Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash							(17)	(63)
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at Beginning of Period			37			95	37	95
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at End of Period	20			32			20	32
Non-Guarantor Subsidiaries
Cash Flows from Operating Activities
Net income attributable to NRG Energy, Inc.	48			(31)			57	66
Net Income	48			(31)			57	67
Income from discontinued operations				0				5
Income from continuing operations				(31)				62
Adjustments to reconcile net income/(loss) to cash provided by operating activities:
Distributions from and equity in losses/(earnings) of unconsolidated affiliates							6	(5)
Depreciation and amortization							60	82
Accretion of asset retirement obligations							27	6
Provision for credit losses							8	11
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 emissions allowances and energy credits							14	7
Amortization of unearned equity compensation							0	0
Net loss on sale of assets and disposal of assets							(1)	2
Impairment losses							47	101
Changes in derivative instruments							20	(12)
Changes in deferred income taxes and liability for uncertain tax benefits							11	(1)
Changes in collateral deposits in support of energy risk management activities							5	(7)
Changes in nuclear decommissioning trust liability							0	0
Changes in other working capital							(923)	(123)
Cash provided/(used) by continuing operations								123
Cash provided/(used) by discontinued operations								(9)
Net Cash Provided/(Used) by Operating Activities							(669)	114
Cash Flows from Investing Activities
Intercompany dividends							0	0
Payments for acquisitions of businesses							(262)	0
Capital expenditures							(28)	(23)
Decrease in notes receivable								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							2	400
Net distributions from investments in unconsolidated affiliates							2	(94)
Contributions to discontinued operations								(44)
Cash (used)/provided by continuing operations								239
Cash used by discontinued operations								(2)
Net Cash (Used)/Provided by Investing Activities							(286)	237
Cash Flows from Financing Activities
Intercompany dividends and transfers							964	(317)
Payments of dividends to common stockholders							0	0
Payments for share repurchase activity							0	0
Payments for debt extinguishment costs								0
Purchase of and distributions to noncontrolling interests from subsidiaries							(2)	(1)
Proceeds from issuance of common stock							0	0
Proceeds from issuance of long-term debt							0	0
Payments of debt issuance costs							0	0
Repayments of long-term debt							(3)	(55)
Net (repayments)/proceeds of Revolving Credit Facility							0	0
Other							0
Cash used by continuing operations								(373)
Cash provided by discontinued operations								43
Net Cash Used by Financing Activities							959	(330)
Effect of exchange rate changes on cash and cash equivalents							(2)
Change in Cash from discontinued operations								32
Net Increase/(Decrease) in Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash							2	(11)
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at Beginning of Period			21			38	21	38
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at End of Period	23			27			23	27
NRG Energy, Inc. (Note Issuer)
Cash Flows from Operating Activities
Net income attributable to NRG Energy, Inc.	249			372			683	1,055
Net Income	249			372			683	1,055
Income from discontinued operations				(2)				385
Income from continuing operations				374				670
Adjustments to reconcile net income/(loss) to cash provided by operating activities:
Distributions from and equity in losses/(earnings) of unconsolidated affiliates							(1,385)	(1,266)
Depreciation and amortization							26	23
Accretion of asset retirement obligations							0	0
Provision for credit losses							0	4
Amortization of nuclear fuel							0	0
Amortization of financing costs and debt discount/premiums							23	20
Loss on debt extinguishment, net							1	47
Amortization of emissions allowances and energy credits							0	0
Amortization of unearned equity compensation							17	15
Net loss on sale of assets and disposal of assets							(5)	3
Impairment losses							0	6
Changes in derivative instruments							0	38
Changes in deferred income taxes and liability for uncertain tax benefits							243	(2)
Changes in collateral deposits in support of energy risk management activities							0	0
Changes in nuclear decommissioning trust liability							0	0
Changes in other working capital							331	(45)
Cash provided/(used) by continuing operations								(487)
Cash provided/(used) by discontinued operations								0
Net Cash Provided/(Used) by Operating Activities							(66)	(487)
Cash Flows from Investing Activities
Intercompany dividends							2,591	3,866
Payments for acquisitions of businesses							0	0
Capital expenditures							(24)	(25)
Decrease in notes receivable								2
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							5	892
Net distributions from investments in unconsolidated affiliates							0
Contributions to discontinued operations								0
Cash (used)/provided by continuing operations								4,735
Cash used by discontinued operations								0
Net Cash (Used)/Provided by Investing Activities							2,572	4,735
Cash Flows from Financing Activities
Intercompany dividends and transfers							(1,661)	(2,725)
Payments of dividends to common stockholders							(221)	(24)
Payments for share repurchase activity							(229)	(1,322)
Payments for debt extinguishment costs								(24)
Purchase of and distributions to noncontrolling interests from subsidiaries							0	0
Proceeds from issuance of common stock							1	3
Proceeds from issuance of long-term debt							59	1,833
Payments of debt issuance costs							(24)	(34)
Repayments of long-term debt							0	(2,432)
Net (repayments)/proceeds of Revolving Credit Facility							(83)	215
Other							0
Cash used by continuing operations								(4,510)
Cash provided by discontinued operations								0
Net Cash Used by Financing Activities							(2,158)	(4,510)
Effect of exchange rate changes on cash and cash equivalents							0
Change in Cash from discontinued operations								0
Net Increase/(Decrease) in Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash							348	(262)
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at Beginning of Period			$ 327			$ 480	327	480
Cash and Cash Equivalents, Funds Deposited by Counterparties and Restricted Cash at End of Period	$ 675			$ 218			$ 675	$ 218