Condensed Consolidated Statements of Comprehensive Income/(Loss) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net loss	$ (642)	$ (276)	$ (845)	$ (229)
Other comprehensive income/(loss), net of tax
Unrealized loss on derivatives, net of income tax expense of $0, $1, $1, and $2	(5)	(3)	(1)	(35)
Foreign currency translation adjustments, net of income tax expense of $0, $0, $0, and $0	1	(3)	8	3
Available-for-sale securities, net of income tax expense of $0, $0, $0, and $0	1	(2)	1	1
Defined benefit plans, net of income tax expense of $0, $0, $0, and $0	27	0	27	1
Other comprehensive income/(loss)	24	(8)	35	(30)
Comprehensive Income/(Loss)	(618)	(284)	(810)	(259)
Less: Comprehensive (loss)/income attributable to noncontrolling interest and redeemable noncontrolling interest	(17)	(16)	(56)	(68)
Comprehensive Income/(Loss) Attributable to NRG Energy, Inc.	(601)	(268)	(754)	(191)
Dividends for preferred shares	0	0	0	5
Gain on redemption of preferred shares	0	(78)	0	(78)
Comprehensive Income/(Loss) Available for Common Stockholders	$ (601)	$ (190)	$ (754)	$ (118)