Consolidated Statement of Stockholders' Equity (USD $) In Millions, unless otherwise specified	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Treasury Stock	Accumulated Other Comprehensive Income/(Loss)	Noncontrolling Interest	NRG Yield	Convertible Preferred Stock [Member]
Balance at Dec. 31, 2011	$ 7,669	$ 3	$ 5,346	$ 3,987	$ (1,924)	$ 74	$ 183		$ 0
Increase (Decrease) in Stockholders' Equity
Net income/(loss) attributable to NRG Energy, Inc.	295
Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest	20
Net income/(loss) attributable to noncontrolling interest	20
Net Income/(Loss)	315
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	91
Other comprehensive income	(224)
Issuance of shares for acquisition of GenOn	2,177	1	2,176
Equity-based compensation	34		34
Preferred stock dividends	9			9
Common stock dividends	41			41
ESPP share purchases	1		(1)	(2)	4
Sales proceeds and other contributions from noncontrolling interests in subsidiaries	347		32
Proceeds from issuance of common stock	0
Other Preferred Stock Dividends and Adjustments	0
Noncontrolling Interest, Increase from Sale of Parent Equity Interest	347						315
Balance at Dec. 31, 2012	10,269	4	7,587	4,230	(1,920)	(150)	518		0
Increase (Decrease) in Stockholders' Equity
Net income/(loss) attributable to NRG Energy, Inc.	(386)
Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest	34
Net income/(loss) attributable to noncontrolling interest	34
Net Income/(Loss)	(352)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(197)
Other comprehensive income	155
Equity-based compensation	36		36
Purchase of treasury stock	25				25
Preferred stock dividends	9			9
Common stock dividends	145			145
ESPP share purchases	8			5	3
Sales proceeds and other contributions from noncontrolling interests in subsidiaries	531
Proceeds from issuance of common stock	16
Other Preferred Stock Dividends and Adjustments	0
NINA deconsolidation	(457)		(217)				(240)
Noncontrolling Interest, Increase from Sale of Parent Equity Interest	73						73
Balance at Dec. 31, 2013	10,467	4	7,840	3,695	(1,942)	5	865		0
Increase (Decrease) in Stockholders' Equity
Net income/(loss) attributable to NRG Energy, Inc.	134
Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest	151						17
Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest	8
Net income/(loss) attributable to noncontrolling interest	(2)
Net Income/(Loss)	132
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(57)					(179)
Other comprehensive income	(189)
Issuance of shares for acquisition of GenOn	401		401
Noncontrolling Interest, Increase from Business Combination	352						352
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders	(57)
Equity-based compensation	45		45
Purchase of treasury stock	44				44
Preferred stock dividends	(9)			9
Common stock dividends	181			181
ESPP share purchases	(1)			(4)	3
Sales proceeds and other contributions from noncontrolling interests in subsidiaries	819
Proceeds from issuance of common stock	21		41				(41)	0
Other Preferred Stock Dividends and Adjustments	(47)			(47)
Non-cash adjustment for issuance of convertible debt	23						23
Noncontrolling Interest, Increase from Sale of Parent Equity Interest	125						125
Noncontrolling Interest, Increase from Subsidiary Equity Issuance	630						630
Balance at Dec. 31, 2014	$ 11,676	$ 4	$ 8,327	$ 3,588	$ (1,983)	$ (174)	$ 1,914		$ 0