Condensed Consolidating Financial Information (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Operating Revenues
Total operating revenues	$ 2,331		$ 2,674		$ 6,359		$ 6,947
Operating Costs and Expenses
Cost of operations	1,726		2,053		4,618		4,985
Depreciation and amortization	239		238		703		665
Impairment charge on emission allowances	0		160		0		160
Selling, general and administrative	253		169		681		479
Acquisition-related transactions and integration costs	18		0		18		0
Development costs	9		11		26		32
Total operating costs and expenses	2,245		2,631		6,046		6,321
Operating Income/(Loss)	86		43		313		626
Other Income/(Expense)
Equity in earnings/(losses) of consolidated subsidiaries	0		0		0		0
Equity in earnings of unconsolidated affiliates	4		16		26		26
Impairment charge on investment	(1)		(3)		(2)		(495)
Other income, net	10		5		14		13
Loss on debt extinguishment	(41)		(32)		(41)		(175)
Interest expense	(163)		(164)		(495)		(504)
Total other expense	(191)		(178)		(498)		(1,135)
Income/(Loss) Before Income Taxes	(105)		(135)		(185)		(509)
Income tax expense	(113)		(80)		(246)		(815)
Net income	8		(55)		61		306
Less: Net income attributable to noncontrolling interest	9		0		18		0
Net Income attributable to NRG Energy, Inc.	(1)		(55)		43		306
Guarantor Subsidiaries
Operating Revenues
Total operating revenues	2,237		2,581		6,058		6,670
Operating Costs and Expenses
Cost of operations	1,701		1,993		4,478		4,791
Depreciation and amortization	217		224		647		626
Impairment charge on emission allowances			160				160
Selling, general and administrative	168		102		421		276
Acquisition-related transactions and integration costs	0				0
Development costs	0		0		0		0
Total operating costs and expenses	2,086		2,479		5,546		5,853
Operating Income/(Loss)	151		102		512		817
Other Income/(Expense)
Equity in earnings/(losses) of consolidated subsidiaries	(10)		6		6		21
Equity in earnings of unconsolidated affiliates	4		2		6		8
Impairment charge on investment	(1)		(3)		(2)		495
Other income, net	1		3		2		3
Loss on debt extinguishment	0		0		0		0
Interest expense	(5)		(20)		(21)		(46)
Total other expense	(11)		(12)		(9)		(509)
Income/(Loss) Before Income Taxes	140		90		503		308
Income tax expense	67		11		193		123
Net income	73		79		310		185
Less: Net income attributable to noncontrolling interest	0				0
Net Income attributable to NRG Energy, Inc.	73		79		310
Non-Guarantor Subsidiaries
Operating Revenues
Total operating revenues	120		97		353		291
Operating Costs and Expenses
Cost of operations	47		63		178		194
Depreciation and amortization	20		10		48		28
Impairment charge on emission allowances			0				0
Selling, general and administrative	14		8		36		20
Acquisition-related transactions and integration costs	0				0
Development costs	0		0		0		(1)
Total operating costs and expenses	81		81		262		241
Operating Income/(Loss)	39		16		91		50
Other Income/(Expense)
Equity in earnings/(losses) of consolidated subsidiaries	1		4		(11)		(5)
Equity in earnings of unconsolidated affiliates	0		14		20		18
Impairment charge on investment	0		0		0		0
Other income, net	2		1		4		6
Loss on debt extinguishment	0		0		0		0
Interest expense	(21)		(13)		(60)		(40)
Total other expense	(18)		6		(47)		(21)
Income/(Loss) Before Income Taxes	21		22		44		29
Income tax expense	(27)		3		(122)		6
Net income	48		19		166		23
Less: Net income attributable to noncontrolling interest	9				18
Net Income attributable to NRG Energy, Inc.	39		19		148
NRG Energy, Inc.
Operating Revenues
Total operating revenues	0		0		0		0
Operating Costs and Expenses
Cost of operations	1		(1)		7		5
Depreciation and amortization	2		4		8		11
Impairment charge on emission allowances			0				0
Selling, general and administrative	74		61		231		185
Acquisition-related transactions and integration costs	18				18
Development costs	9		11		26		33
Total operating costs and expenses	104		75		290		234
Operating Income/(Loss)	(104)		(75)		(290)		(234)
Other Income/(Expense)
Equity in earnings/(losses) of consolidated subsidiaries	121		88		463		185
Equity in earnings of unconsolidated affiliates	0		0		0		0
Impairment charge on investment	0		0		0		0
Other income, net	7		1		8		4
Loss on debt extinguishment	(41)		(32)		(41)		(175)
Interest expense	(137)		(131)		(414)		(418)
Total other expense	(50)		(74)		16		(404)
Income/(Loss) Before Income Taxes	(154)		(149)		(274)		(638)
Income tax expense	(153)		(94)		(317)		(944)
Net income	(1)		(55)		43		306
Less: Net income attributable to noncontrolling interest	0				0
Net Income attributable to NRG Energy, Inc.	(1)		(55)		43
Eliminations
Operating Revenues
Total operating revenues	(26)	[1]	(4)	[1]	(52)	[1]	(14)	[1]
Operating Costs and Expenses
Cost of operations	(23)	[1]	(2)	[1]	(45)	[1]	(5)	[1]
Depreciation and amortization	0	[1]	0	[1]	0	[1]	0	[1]
Impairment charge on emission allowances			0	[1]			0	[1]
Selling, general and administrative	(3)	[1]	(2)	[1]	(7)	[1]	(2)	[1]
Acquisition-related transactions and integration costs	0	[1]			0	[1]
Development costs	0	[1]	0	[1]	0	[1]	0	[1]
Total operating costs and expenses	(26)	[1]	(4)	[1]	(52)	[1]	(7)	[1]
Operating Income/(Loss)	0	[1]	0	[1]	0	[1]	(7)	[1]
Other Income/(Expense)
Equity in earnings/(losses) of consolidated subsidiaries	(112)	[1]	(98)	[1]	(458)	[1]	(201)	[1]
Equity in earnings of unconsolidated affiliates	0	[1]	0	[1]	0	[1]	0	[1]
Impairment charge on investment	0	[1]	0	[1]	0	[1]	0	[1]
Other income, net	0	[1]	0	[1]	0	[1]	0	[1]
Loss on debt extinguishment	0	[1]	0	[1]	0	[1]	0	[1]
Interest expense	0	[1]	0	[1]	0	[1]	0	[1]
Total other expense	(112)	[1]	(98)	[1]	(458)	[1]	(201)	[1]
Income/(Loss) Before Income Taxes	(112)	[1]	(98)	[1]	(458)	[1]	(208)	[1]
Income tax expense	0	[1]	0	[1]	0	[1]	0	[1]
Net income	(112)	[1]	(98)		(458)	[1]	(208)	[1]
Less: Net income attributable to noncontrolling interest	0	[1]			0	[1]
Net Income attributable to NRG Energy, Inc.	$ (112)	[1]	$ (98)	[1]	$ (458)	[1]

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