Consolidated Statements of Comprehensive Income (USD $) In Millions, 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
Net Income/(Loss)	$ 97	$ 182	$ (80)	$ (67)	$ (290)	$ 138	$ 131	$ (331)	$ 132	$ (352)	$ 315
Other Comprehensive (Loss)/Income, net of tax
Unrealized (loss)/gain on derivatives, net of income tax benefit of $21, $6, and $94									(45)	8	(163)
Foreign currency translation adjustments, net of income tax benefit of $5, $14, and $1									(8)	(24)	(1)
Reclassification adjustment for translation gain realized upon sale of Schkopau, net of income tax benefit of $0, $0, and $6									0	0	(11)
Available-for-sale securities, net of income tax benefit/(expense) of $2, $(2), and $(1)									(7)	3	3
Defined benefit plan, net of income tax benefit/(expense) of $88, $(100), and $21									(129)	168	(52)
Other comprehensive (loss)/income									(189)	155	(224)
Comprehensive (Loss)/Income									(57)	(197)	91	91
Less: Comprehensive income attributable to noncontrolling interests and redeemable noncontrolling interests									(8)	(34)	(20)	(20)
Less: Net (loss)/income attributable to noncontrolling interests and redeemable noncontrolling interests									(2)	34	20
Comprehensive (Loss)/Income Attributable to NRG Energy, Inc.									(65)	(231)	71
Dividends for preferred shares									56	9	9
Dividends, Preferred Stock, Cash									9	(9)	(9)
Comprehensive (Loss)/Income Available for Common Stockholders									$ (121)	$ (240)	$ 62