Earnings Per Share (Details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($) $ / shares shares	Sep. 30, 2016 USD ($) $ / shares shares	Jun. 30, 2016 USD ($) $ / shares shares	Mar. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) $ / shares shares	Jun. 30, 2015 USD ($) $ / shares shares	Mar. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Jun. 13, 2016	May 24, 2016
Temporary Equity, Redemption Percentage												1.00	1.00
Numerator:
Net (loss)/income attributable to NRG Energy, Inc.	$ (987)	$ 402	$ (271)	$ 82	$ (6,314)	$ 66	$ (14)	$ (120)	$ (774)	$ (6,382)	$ 134
Preferred Stock Dividends, Income Statement Impact									5	20	56
Redeemable Preferred Stock Dividends											9
Other Preferred Stock Dividends and Adjustments									0	0	47
Gain on Redemption of Redeemable Preferred Stock			78						(78)	0	0
(Loss)/Income Available for Common Stockholders	$ (987)	$ 402	$ (193)	$ 77	$ (6,319)	$ 61	$ (19)	$ (125)	$ (701)	$ (6,402)	$ 78
Denominator (Basic EPS):
Weighted average number of common shares outstanding | shares	316	316	315	315	315	331	333	336	316	329	334
Basic earnings per share:
(Loss)/Earnings per weighted average common share — basic | $ / shares	$ (3.13)	$ 1.27	$ (0.61)	$ 0.24	$ (20.08)	$ 0.18	$ (0.06)	$ 0.37	$ (2.22)	$ (19.46)	$ 0.23
Denominator (Diluted EPS):
Incremental shares attributable to the issuance of equity compensation (treasury stock method) | shares									0	0	5
Total dilutive shares | shares	316	317	315	315	315	332	333	336	316	329	339
Diluted earnings per share:
(Loss)/Earnings per weighted average common share — diluted | $ / shares	$ (3.13)	$ 1.27	$ (0.61)	$ 0.24	$ (20.08)	$ 0.18	$ (0.06)	$ (0.37)	$ (2.22)	$ (19.46)	$ 0.23