Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net (Loss)/Income	$ (1,055)	$ 393	$ (276)	$ 47	$ (6,358)	$ 67	$ (9)	$ (136)	$ (891)	$ (6,436)	$ 132
Other Comprehensive Income/(Loss), net of tax
Unrealized gain/(loss) on derivatives, net of income tax expense/(benefit) of $1, $19, and $(21)									35	(15)	(45)
Foreign currency translation adjustments, net of income tax benefit of $0, $0, and $5									(1)	(11)	(8)
Available-for-sale securities, net of income tax benefit of $0, $3, and $2									1	17	(7)
Defined benefit plan, net of income tax expense/(benefit) of $0, $69, and $(88)									3	10	(129)
Other comprehensive income/(loss)									38	1	(189)
Comprehensive Loss									(853)	(6,435)	(57)
Less: Comprehensive (loss)/income attributable to noncontrolling interests and redeemable noncontrolling interests									(117)	(73)	8
Comprehensive Loss Attributable to NRG Energy, Inc.									(736)	(6,362)	(65)
Preferred Stock Dividends, Income Statement Impact									5	20	56
Gain on Redemption of Redeemable Preferred Stock			$ 78						(78)	0	0
Comprehensive Loss Available for Common Stockholders									$ (663)	$ (6,382)	$ (121)