Condensed Consolidating Financial Information (Details 3) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012		Jun. 30, 2012		Dec. 31, 2011
Current Assets
Cash and cash equivalents	$ 1,368		$ 2,087		$ 1,149		$ 1,105
Funds deposited by counterparties	134		271
Restricted cash	267		217
Accounts receivable-trade, net	1,290		1,061
Inventory	874		911
Derivative instruments	1,853		2,644
Deferred income taxes	10		56
Cash collateral paid in support of energy risk management activities	387		229
Renewable energy grant receivable	345		58
Prepayments and other current assets	415		401
Total current assets	6,943		7,935
Net property, plant and equipment	20,454		20,241
Other Assets
Investment in subsidiaries	0		0
Equity investments in affiliates	639		676
Capital leases and notes receivable, less current portion	70		79
Goodwill	1,954		1,956
Intangible assets, net	1,120		1,200
Nuclear decommissioning trust fund	503		473
Deferred income taxes	1,644		1,288
Derivative instruments	587		662
Other non-current assets	578		600
Total other assets	7,095		6,934
Total assets	34,492		35,110
Current Liabilities
Current portion of long-term debt and capital leases	737		147
Accounts payable	1,196		1,171
Accounts payable — affiliate	0		0
Derivative instruments	1,512		1,981
Deferred income taxes	0
Cash collateral received in support of energy risk management activities	134		271
Accrued expenses and other current liabilities	832		1,100
Total current liabilities	4,411		4,670
Other Liabilities
Long-term debt and capital leases	15,889		15,736
Nuclear decommissioning reserve	287		354
Nuclear decommissioning trust liability	287		273
Deferred income taxes	47		55
Derivative instruments	420		500
Out-of-market contracts	1,182		1,231
Other non-current liabilities	1,417		1,555
Total non-current liabilities	19,529		19,704
Total Liabilities	23,940		24,374
3.625% convertible perpetual preferred stock	249		249
3.625% convertible perpetual preferred stock, interest rate (as a percentage)	3.625%		3.625%		3.625%
Total Stockholders' Equity	10,303		10,487
Total Liabilities and Stockholders' Equity	34,492		35,110
Guarantor Subsidiaries
Current Assets
Cash and cash equivalents	72		78		694		44
Funds deposited by counterparties	0		131
Restricted cash	12		11
Accounts receivable-trade, net	1,034		807
Inventory	428		472
Derivative instruments	1,352		2,058
Deferred income taxes	(222)		(153)
Cash collateral paid in support of energy risk management activities	338		81
Renewable energy grant receivable	0		0
Prepayments and other current assets	3,208		2,966
Total current assets	6,222		6,451
Net property, plant and equipment	9,558		9,905
Other Assets
Investment in subsidiaries	221		244
Equity investments in affiliates	32		33
Capital leases and notes receivable, less current portion	0		3
Goodwill	1,941		1,944
Intangible assets, net	956		1,042
Nuclear decommissioning trust fund	503		473
Deferred income taxes	(914)		(915)
Derivative instruments	233		149
Other non-current assets	80		85
Total other assets	3,052		3,058
Total assets	18,832		19,414
Current Liabilities
Current portion of long-term debt and capital leases	1		1
Accounts payable	652		541
Accounts payable — affiliate	(321)		(55)
Derivative instruments	1,324		1,726
Deferred income taxes	0
Cash collateral received in support of energy risk management activities	0		131
Accrued expenses and other current liabilities	256		354
Total current liabilities	1,912		2,698
Other Liabilities
Long-term debt and capital leases	313		310
Nuclear decommissioning reserve	287		354
Nuclear decommissioning trust liability	287		273
Deferred income taxes	47		0
Derivative instruments	320		312
Out-of-market contracts	167		180
Other non-current liabilities	521		618
Total non-current liabilities	1,942		2,047
Total Liabilities	3,854		4,745
3.625% convertible perpetual preferred stock	0		0
Total Stockholders' Equity	14,978		14,669
Total Liabilities and Stockholders' Equity	18,832		19,414
Non-Guarantor Subsidiaries
Current Assets
Cash and cash equivalents	475		1,258		58		85
Funds deposited by counterparties	134		140
Restricted cash	239		196
Accounts receivable-trade, net	256		254
Inventory	446		439
Derivative instruments	523		604
Deferred income taxes	(121)		10
Cash collateral paid in support of energy risk management activities	49		148
Renewable energy grant receivable	345		58
Prepayments and other current assets	169		(57)
Total current assets	2,515		3,050
Net property, plant and equipment	10,776		10,235
Other Assets
Investment in subsidiaries	447		(102)
Equity investments in affiliates	712		633
Capital leases and notes receivable, less current portion	59		74
Goodwill	13		12
Intangible assets, net	183		177
Nuclear decommissioning trust fund	0		0
Deferred income taxes	2,022		1,829
Derivative instruments	357		515
Other non-current assets	265		305
Total other assets	4,058		3,443
Total assets	17,349		16,728
Current Liabilities
Current portion of long-term debt and capital leases	775		137
Accounts payable	517		584
Accounts payable — affiliate	1,918		1,421
Derivative instruments	209		271
Deferred income taxes	0
Cash collateral received in support of energy risk management activities	134		140
Accrued expenses and other current liabilities	346		503
Total current liabilities	3,899		3,056
Other Liabilities
Long-term debt and capital leases	8,045		8,459
Nuclear decommissioning reserve	0		0
Nuclear decommissioning trust liability	0		0
Deferred income taxes	0		55
Derivative instruments	103		190
Out-of-market contracts	1,046		1,082
Other non-current liabilities	655		802
Total non-current liabilities	9,849		10,588
Total Liabilities	13,748		13,644
3.625% convertible perpetual preferred stock	0		0
Total Stockholders' Equity	3,601		3,084
Total Liabilities and Stockholders' Equity	17,349		16,728
NRG Energy, Inc.
Current Assets
Cash and cash equivalents	821		751		397		976
Funds deposited by counterparties	0		0
Restricted cash	16		10
Accounts receivable-trade, net	0		0
Inventory	0		0
Derivative instruments	0		0
Deferred income taxes	353		199
Cash collateral paid in support of energy risk management activities	0		0
Renewable energy grant receivable	0		0
Prepayments and other current assets	(2,886)		(2,518)
Total current assets	(1,696)		(1,558)
Net property, plant and equipment	143		121
Other Assets
Investment in subsidiaries	17,222		17,655
Equity investments in affiliates	10		10
Capital leases and notes receivable, less current portion	241		531
Goodwill	0		0
Intangible assets, net	33		33
Nuclear decommissioning trust fund	0		0
Deferred income taxes	536		374
Derivative instruments	0		0
Other non-current assets	233		210
Total other assets	18,275		18,813
Total assets	16,722		17,376
Current Liabilities
Current portion of long-term debt and capital leases	20		15
Accounts payable	27		46
Accounts payable — affiliate	(1,580)		(1,366)
Derivative instruments	0		2
Deferred income taxes	0
Cash collateral received in support of energy risk management activities	0		0
Accrued expenses and other current liabilities	230		243
Total current liabilities	(1,303)		(1,060)
Other Liabilities
Long-term debt and capital leases	7,762		7,496
Nuclear decommissioning reserve	0		0
Nuclear decommissioning trust liability	0		0
Deferred income taxes	0		0
Derivative instruments	0		0
Out-of-market contracts	0		0
Other non-current liabilities	241		135
Total non-current liabilities	8,003		7,631
Total Liabilities	6,700		6,571
3.625% convertible perpetual preferred stock	249		249
3.625% convertible perpetual preferred stock, interest rate (as a percentage)	3.625%		3.625%
Total Stockholders' Equity	9,773		10,556
Total Liabilities and Stockholders' Equity	16,722		17,376
Eliminations
Current Assets
Cash and cash equivalents	0	[1]	0	[1]	0	[1]	0	[1]
Funds deposited by counterparties	0	[1]	0	[1]
Restricted cash	0	[1]	0	[1]
Accounts receivable-trade, net	0	[1]	0	[1]
Inventory	0	[1]	0	[1]
Derivative instruments	(22)	[1]	(18)	[1]
Deferred income taxes	0	[1]	0	[1]
Cash collateral paid in support of energy risk management activities	0	[1]	0	[1]
Renewable energy grant receivable	0		0	[1]
Prepayments and other current assets	(76)	[1]	10	[1]
Total current assets	(98)	[1]	(8)	[1]
Net property, plant and equipment	(23)	[1]	(20)	[1]
Other Assets
Investment in subsidiaries	(17,890)	[1]	(17,797)	[1]
Equity investments in affiliates	(115)	[1]	0	[1]
Capital leases and notes receivable, less current portion	(230)	[1]	(529)	[1]
Goodwill	0	[1]	0	[1]
Intangible assets, net	(52)	[1]	(52)	[1]
Nuclear decommissioning trust fund	0	[1]	0	[1]
Deferred income taxes	0	[1]	0	[1]
Derivative instruments	(3)	[1]	(2)	[1]
Other non-current assets	0	[1]	0	[1]
Total other assets	(18,290)	[1]	(18,380)	[1]
Total assets	(18,411)	[1]	(18,408)	[1]
Current Liabilities
Current portion of long-term debt and capital leases	(59)	[1]	(6)	[1]
Accounts payable	0	[1]	0	[1]
Accounts payable — affiliate	(17)	[1]	0	[1]
Derivative instruments	(21)	[1]	(18)	[1]
Deferred income taxes	0	[1]
Cash collateral received in support of energy risk management activities	0	[1]	0	[1]
Accrued expenses and other current liabilities	0	[1]	0	[1]
Total current liabilities	(97)	[1]	(24)	[1]
Other Liabilities
Long-term debt and capital leases	(231)	[1]	(529)	[1]
Nuclear decommissioning reserve	0	[1]	0	[1]
Nuclear decommissioning trust liability	0	[1]	0	[1]
Deferred income taxes	0	[1]	0	[1]
Derivative instruments	(3)	[1]	(2)	[1]
Out-of-market contracts	(31)	[1]	(31)	[1]
Other non-current liabilities	0	[1]	0	[1]
Total non-current liabilities	(265)	[1]	(562)	[1]
Total Liabilities	(362)	[1]	(586)	[1]
3.625% convertible perpetual preferred stock	0	[1]	0	[1]
Total Stockholders' Equity	(18,049)	[1]	(17,822)	[1]
Total Liabilities and Stockholders' Equity	$ (18,411)	[1]	$ (18,408)	[1]

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