Condensed Consolidating Financial Information (Details 5) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Condensed Financial Statements
Sale proceeds and other contributions from noncontrolling interest in subsidiaries					$ 316		$ 0
Cash Flows from Operating Activities
Net income	8		(55)		61		306
Adjustments to reconcile net income to net cash provided by operating activities:
Distributions and equity in (earnings)/losses of unconsolidated affiliates					8		8
Depreciation and amortization	239		238		703		665
Provision for bad debts					40		41
Amortization of nuclear fuel					29		31
Amortization of financing costs and debt discount/premiums					25		25
Loss on debt extinguishment					8		58
Amortization of intangibles and out-of-market commodity contracts					108		118
Amortization of unearned equity compensation					27		14
Changes in deferred income taxes and liability for uncertain tax benefits					(261)		(829)
Changes in nuclear decommissioning trust liability					25		20
Changes in derivative instruments					360		(201)
Changes in collateral deposits supporting energy risk management activities					213		7
Impairment charge on investment					0		(481)
Impairment charge on emission allowances	0		160		0		160
Cash used by changes in other working capital					(288)		(236)
Net Cash (Used)/Provided/ by Operating Activities					1,058		668
Cash Flows from Investing Activities
Intercompany loans to subsidiaries					0		0
Acquisitions of businesses, net of cash acquired	(40)				(40)		(352)
Capital expenditures					(2,474)		(1,355)
Increase in restricted cash, net					(96)		(92)
Decrease/(Increase) in restricted cash to support equity requirements for U.S. DOE funded projects					151		(316)
Decrease in notes receivable					(22)		27
Purchases of emission allowances					(8)		(27)
Proceeds from sale of emission allowances					8		6
Investments in nuclear decommissioning trust fund securities					(341)		(314)
Proceeds from sales of nuclear decommissioning trust fund securities					316		294
Proceeds from sale of assets, net of cash disposed of					137		14
Investments in unconsolidated affiliates					0		(17)
Proceeds from renewable energy grants					49		0
Other					(9)		(29)
Net Cash Used by Investing Activities					(2,329)		(2,161)
Cash Flows from Financing Activities
Proceeds from intercompany loans					0		0
Payment of dividends to common and preferred stockholders					(28)		(7)
Payment of intercompany dividends					0		0
Payment for treasury stock					0		(378)
Net payments for settlement of acquired derivatives that include financing elements					(65)		(61)
Proceeds from issuance of long-term debt					2,541		5,710
Decrease in restricted cash supporting funded letter of credit							1,300
Payment for settlement of funded letter of credit facility					0		(1,300)
Proceeds from issuance of common stock							2
Payment of debt issuance and hedging costs					(30)		(149)
Payments for short and long-term debt					(955)		(5,450)
Net Cash Provided/(Used) by Financing Activities					1,779		(333)
Effect of exchange rate changes on cash and cash equivalents					(3)		2
Net (Decrease)/Increase in Cash and Cash Equivalents					505		(1,824)
Cash and Cash Equivalents at Beginning of Period					1,105		2,951
Cash and Cash Equivalents at End of Period	1,610		1,127		1,610		1,127
Guarantor Subsidiaries
Condensed Financial Statements
Sale proceeds and other contributions from noncontrolling interest in subsidiaries					0
Cash Flows from Operating Activities
Net income	73		79		310		185
Adjustments to reconcile net income to net cash provided by operating activities:
Distributions and equity in (earnings)/losses of unconsolidated affiliates					(6)		(10)
Depreciation and amortization	217		224		647		626
Provision for bad debts					40		41
Amortization of nuclear fuel					29		31
Amortization of financing costs and debt discount/premiums					0		0
Loss on debt extinguishment					0		0
Amortization of intangibles and out-of-market commodity contracts					107		118
Amortization of unearned equity compensation					0		0
Changes in deferred income taxes and liability for uncertain tax benefits					193		123
Changes in nuclear decommissioning trust liability					25		20
Changes in derivative instruments					360		(199)
Changes in collateral deposits supporting energy risk management activities					213		5
Impairment charge on investment							(481)
Impairment charge on emission allowances			160				160
Cash used by changes in other working capital					24		(1,182)
Net Cash (Used)/Provided/ by Operating Activities					1,942		399
Cash Flows from Investing Activities
Intercompany loans to subsidiaries					(1,686)		(191)
Acquisitions of businesses, net of cash acquired	0						0
Capital expenditures					(183)		(295)
Increase in restricted cash, net					(2)		(54)
Decrease/(Increase) in restricted cash to support equity requirements for U.S. DOE funded projects					0		0
Decrease in notes receivable					0		0
Purchases of emission allowances					(8)		(27)
Proceeds from sale of emission allowances					8		6
Investments in nuclear decommissioning trust fund securities					(341)		(314)
Proceeds from sales of nuclear decommissioning trust fund securities					316		294
Proceeds from sale of assets, net of cash disposed of					133		14
Investments in unconsolidated affiliates							(1)
Proceeds from renewable energy grants					3
Other					13		(11)
Net Cash Used by Investing Activities					(1,747)		(579)
Cash Flows from Financing Activities
Proceeds from intercompany loans					0		38
Payment of dividends to common and preferred stockholders					0		0
Payment of intercompany dividends					(172)		(65)
Payment for treasury stock							0
Net payments for settlement of acquired derivatives that include financing elements					(65)		(61)
Proceeds from issuance of long-term debt					9		116
Decrease in restricted cash supporting funded letter of credit							0
Payment for settlement of funded letter of credit facility							0
Proceeds from issuance of common stock							0
Payment of debt issuance and hedging costs					0		0
Payments for short and long-term debt					0		0
Net Cash Provided/(Used) by Financing Activities					(228)		28
Effect of exchange rate changes on cash and cash equivalents					0		0
Net (Decrease)/Increase in Cash and Cash Equivalents					(33)		(152)
Cash and Cash Equivalents at Beginning of Period					44		168
Cash and Cash Equivalents at End of Period	11		16		11		16
Non-Guarantor Subsidiaries
Condensed Financial Statements
Sale proceeds and other contributions from noncontrolling interest in subsidiaries					316
Cash Flows from Operating Activities
Net income	48		19		166		23
Adjustments to reconcile net income to net cash provided by operating activities:
Distributions and equity in (earnings)/losses of unconsolidated affiliates					19		2
Depreciation and amortization	20		10		48		28
Provision for bad debts					0		0
Amortization of nuclear fuel					0		0
Amortization of financing costs and debt discount/premiums					8		5
Loss on debt extinguishment					0		0
Amortization of intangibles and out-of-market commodity contracts					1		0
Amortization of unearned equity compensation					0		0
Changes in deferred income taxes and liability for uncertain tax benefits					(122)		6
Changes in nuclear decommissioning trust liability					0		0
Changes in derivative instruments					0		1
Changes in collateral deposits supporting energy risk management activities					0		2
Impairment charge on investment							0
Impairment charge on emission allowances			0				0
Cash used by changes in other working capital					57		211
Net Cash (Used)/Provided/ by Operating Activities					177		278
Cash Flows from Investing Activities
Intercompany loans to subsidiaries					416		0
Acquisitions of businesses, net of cash acquired	(17)						(91)
Capital expenditures					(2,241)		(1,027)
Increase in restricted cash, net					(94)		(38)
Decrease/(Increase) in restricted cash to support equity requirements for U.S. DOE funded projects					113		(254)
Decrease in notes receivable					(20)		27
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 sales of nuclear decommissioning trust fund securities					0		0
Proceeds from sale of assets, net of cash disposed of					0		0
Investments in unconsolidated affiliates							(16)
Proceeds from renewable energy grants					46
Other					(8)		(8)
Net Cash Used by Investing Activities					(1,805)		(1,407)
Cash Flows from Financing Activities
Proceeds from intercompany loans					0		448
Payment of dividends to common and preferred stockholders					0		0
Payment of intercompany dividends					(6)		(1,304)
Payment for treasury stock							0
Net payments for settlement of acquired derivatives that include financing elements					0		0
Proceeds from issuance of long-term debt					1,526		798
Decrease in restricted cash supporting funded letter of credit							1,300
Payment for settlement of funded letter of credit facility
Proceeds from issuance of common stock							0
Payment of debt issuance and hedging costs					(16)		(41)
Payments for short and long-term debt					(51)		(77)
Net Cash Provided/(Used) by Financing Activities					1,769		1,124
Effect of exchange rate changes on cash and cash equivalents					(3)		2
Net (Decrease)/Increase in Cash and Cash Equivalents					138		(3)
Cash and Cash Equivalents at Beginning of Period					85		111
Cash and Cash Equivalents at End of Period	223		108		223		108
NRG Energy, Inc.
Condensed Financial Statements
Sale proceeds and other contributions from noncontrolling interest in subsidiaries					0
Cash Flows from Operating Activities
Net income	(1)		(55)		43		306
Adjustments to reconcile net income to net cash provided by operating activities:
Distributions and equity in (earnings)/losses of unconsolidated affiliates					285		1,184
Depreciation and amortization	2		4		8		11
Provision for bad debts					0		0
Amortization of nuclear fuel					0		0
Amortization of financing costs and debt discount/premiums					17		20
Loss on debt extinguishment					8		58
Amortization of intangibles and out-of-market commodity contracts					0		0
Amortization of unearned equity compensation					27		14
Changes in deferred income taxes and liability for uncertain tax benefits					(332)		(958)
Changes in nuclear decommissioning trust liability					0		0
Changes in derivative instruments					0		(3)
Changes in collateral deposits supporting energy risk management activities					0		0
Impairment charge on investment							0
Impairment charge on emission allowances			0				0
Cash used by changes in other working capital					(369)		728
Net Cash (Used)/Provided/ by Operating Activities					(883)		1,360
Cash Flows from Investing Activities
Intercompany loans to subsidiaries					0		(486)
Acquisitions of businesses, net of cash acquired	(23)						(261)
Capital expenditures					(50)		(33)
Increase in restricted cash, net					0		0
Decrease/(Increase) in restricted cash to support equity requirements for U.S. DOE funded projects					38		(62)
Decrease in notes receivable					(2)		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 sales of nuclear decommissioning trust fund securities					0		0
Proceeds from sale of assets, net of cash disposed of					(4)		0
Investments in unconsolidated affiliates							0
Proceeds from renewable energy grants					0
Other					(14)		(10)
Net Cash Used by Investing Activities					(47)		(852)
Cash Flows from Financing Activities
Proceeds from intercompany loans					1,270		191
Payment of dividends to common and preferred stockholders					(28)		(7)
Payment of intercompany dividends					0		0
Payment for treasury stock							(378)
Net payments for settlement of acquired derivatives that include financing elements					0		0
Proceeds from issuance of long-term debt					1,006		4,796
Decrease in restricted cash supporting funded letter of credit							0
Payment for settlement of funded letter of credit facility							(1,300)
Proceeds from issuance of common stock							2
Payment of debt issuance and hedging costs					(14)		(108)
Payments for short and long-term debt					(904)		(5,373)
Net Cash Provided/(Used) by Financing Activities					1,330		(2,177)
Effect of exchange rate changes on cash and cash equivalents					0		0
Net (Decrease)/Increase in Cash and Cash Equivalents					400		(1,669)
Cash and Cash Equivalents at Beginning of Period					976		2,672
Cash and Cash Equivalents at End of Period	1,376		1,003		1,376		1,003
Eliminations
Condensed Financial Statements
Sale proceeds and other contributions from noncontrolling interest in subsidiaries					0	[1]
Cash Flows from Operating Activities
Net income	(112)	[1]	(98)		(458)	[1]	(208)	[1]
Adjustments to reconcile net income to net cash provided by operating activities:
Distributions and equity in (earnings)/losses of unconsolidated affiliates					280	[1]	(1,168)	[1]
Depreciation and amortization	0	[1]	0	[1]	0	[1]	0	[1]
Provision for bad debts					0	[1]	0	[1]
Amortization of nuclear fuel					0	[1]	0	[1]
Amortization of financing costs and debt discount/premiums					0	[1]	0
Loss on debt extinguishment					0	[1]	0	[1]
Amortization of intangibles and out-of-market commodity contracts					0	[1]	0	[1]
Amortization of unearned equity compensation					0	[1]	0	[1]
Changes in deferred income taxes and liability for uncertain tax benefits					0	[1]	0	[1]
Changes in nuclear decommissioning trust liability					0	[1]	0	[1]
Changes in derivative instruments					0	[1]	0	[1]
Changes in collateral deposits supporting energy risk management activities					0	[1]	0	[1]
Impairment charge on investment							0	[1]
Impairment charge on emission allowances			0	[1]			0	[1]
Cash used by changes in other working capital					0	[1]	7	[1]
Net Cash (Used)/Provided/ by Operating Activities					(178)	[1]	(1,369)	[1]
Cash Flows from Investing Activities
Intercompany loans to subsidiaries					1,270	[1]	677	[1]
Acquisitions of businesses, net of cash acquired	0	[1]					0	[1]
Capital expenditures					0	[1]	0	[1]
Increase in restricted cash, net					0	[1]	0	[1]
Decrease/(Increase) in restricted cash to support equity requirements for U.S. DOE funded projects					0	[1]	0	[1]
Decrease in notes receivable					0	[1]	0	[1]
Purchases of emission allowances					0	[1]	0
Proceeds from sale of emission allowances					0	[1]	0
Investments in nuclear decommissioning trust fund securities					0	[1]	0	[1]
Proceeds from sales of nuclear decommissioning trust fund securities					0	[1]	0	[1]
Proceeds from sale of assets, net of cash disposed of					0	[1]	0
Investments in unconsolidated affiliates							0
Proceeds from renewable energy grants					0	[1]
Other					0	[1]	0	[1]
Net Cash Used by Investing Activities					1,270	[1]	677	[1]
Cash Flows from Financing Activities
Proceeds from intercompany loans					(1,270)	[1]	(677)	[1]
Payment of dividends to common and preferred stockholders					0	[1]	0	[1]
Payment of intercompany dividends					178	[1]	1,369	[1]
Payment for treasury stock							0	[1]
Net payments for settlement of acquired derivatives that include financing elements					0	[1]	0	[1]
Proceeds from issuance of long-term debt					0	[1]	0	[1]
Decrease in restricted cash supporting funded letter of credit							0	[1]
Payment for settlement of funded letter of credit facility							0
Proceeds from issuance of common stock							0	[1]
Payment of debt issuance and hedging costs					0	[1]	0	[1]
Payments for short and long-term debt					0	[1]	0	[1]
Net Cash Provided/(Used) by Financing Activities					(1,092)	[1]	692	[1]
Effect of exchange rate changes on cash and cash equivalents					0	[1]	0	[1]
Net (Decrease)/Increase in Cash and Cash Equivalents					0	[1]	0	[1]
Cash and Cash Equivalents at Beginning of Period					0	[1]	0	[1]
Cash and Cash Equivalents at End of Period	$ 0	[1]	$ 0	[1]	$ 0	[1]	$ 0	[1]

[1] All significant intercompany transactions have been eliminated in consolidation.