Condensed Consolidated Statements of Comprehensive Loss (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2013	Sep. 30, 2012
Net Income/(Loss)	$ 143	$ 8		$ (47)	$ 61
Other Comprehensive (Loss)/Income, net of tax
Unrealized (loss)/gain on derivatives, net of income tax benefit of $5, $24, $2 and $76	(16)	(43)		8	(132)
Foreign currency translation adjustments, net of income tax benefit of $1, $0, $13 and $1	5	1		(14)	(1)
Reclassification adjustment for translation gain realized upon sale of Schkopau, net of income tax expense of $0, $6, $0 and $6	0	(11)		0	(11)
Available-for-sale securities, net of income tax expense of $0, $1, $1 and $1	0	2	2	2	2
Defined benefit plans, net of tax expense of $0, $0, $4 and $0	0	0		25	0
Other comprehensive (loss)/income	(11)	(51)		21	(142)
Comprehensive Income/(Loss)	132	(43)		(26)	(81)
Less: Comprehensive income attributable to noncontrolling interest	(18)	(9)		(26)	(18)
Comprehensive Income/(Loss) Attributable to NRG Energy, Inc.	114	(52)		(52)	(99)
Dividends for preferred shares	2	2		7	7
Comprehensive Income/(Loss) Available for Common Stockholders	$ 112	$ (54)		$ (59)	$ (106)