Consolidated Statements of Operations (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Operating Revenues
Total operating revenues	$ 4,192	$ 4,569	$ 3,621	$ 3,486	$ 2,795	$ 3,490	$ 2,929	$ 2,081	$ 15,868	[1]	$ 11,295	[2]	$ 8,422	[3]
Total operating revenues
Cost of operations									11,779		8,121		6,140
Depreciation and amortization									1,523		1,256		950
Impairment losses									97		459		0
Selling, general and administrative									1,042		904		807
Acquisition-related transaction and integration costs									84		128		107
Research and Development Expense									91		84		68
Total operating costs and expenses									14,616		10,952		8,072
Gain on sale of assets									19		0		0
Operating Income	453	549	89	180	(205)	527	287	(266)	1,271		343		350
Other Income/(Expense)
Equity in earnings of unconsolidated affiliates									38		7		37
Bargain purchase gain related to GenOn acquisition									0		0		296
Impairment losses on investments									0		(99)		(2)
Other income, net									22		13		19
Gain on Sale of Investments									18		0		0
Loss on debt extinguishment									(95)		(50)		(51)
Interest expense									(1,119)		(848)		(661)
Total other expense									(1,136)		(977)		(362)
Income/(Loss)Before Income Taxes									135		(634)		(12)
Income tax expense/(benefit)									3		(282)		(327)
Net Income/(Loss)	97	182	(80)	(67)	(290)	138	131	(331)	132		(352)		315
Less: Net (loss)/income attributable to noncontrolling interests and redeemable noncontrolling interests									(2)		34		20
Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest									8		34		20		20
Net Income/(Loss) Attributable to NRG Energy, Inc.	119	168	(97)	(56)	(297)	119	124	(332)	134		(386)		295
Dividends for preferred shares									56		9		9
Dividends, Preferred Stock, Cash									9		(9)		(9)
Income/(Loss) Available for Common Stockholders									$ 78		$ (395)		$ 286
Earnings/(Loss) Per Share Attributable to NRG Energy, Inc. Common Stockholders
Weighted average number of common shares outstanding - basic (in shares)	338	338	337	324	323	323	323	323	334		323		232
Net Income/(Loss) per Weighted Average Common Share - Basic (in dollars per share)	$ 0.21	$ 0.49	$ (0.30)	$ (0.18)	$ (0.92)	$ 0.36	$ 0.37	$ (1.03)	$ 0.23		$ (1.22)		$ 1.23
Weighted average number of common shares outstanding - diluted (in shares)	342	343	337	324	323	327	327	323	339		323		234
Net Income/(Loss) Per Weighted Average Common Share - Diluted (in dollars per share)	$ 0.20	$ 0.48	$ (0.30)	$ (0.18)	$ (0.92)	$ 0.36	$ 0.37	$ (1.03)	$ 0.23		$ (1.22)		$ 1.22
Dividends Per Common Share									$ 0.54		$ 0.45		$ 0.18

[1] (a) Operating revenues include inter-segment sales and net derivative gains and losses of:$1,836 $9 $— $7 $— $62 $— $1,914

[2] (d) Operating revenues include inter-segment sales and net derivative gains and losses of:$2,230 $9 $— $7 $— $61 $— $2,307

[3] (f) Operating revenues include inter-segment sales and net derivative gains and losses of:$1,819 $5 $— $4 $— $10 $— $1,838