Consolidated Statements of Operations - USD ($) shares in Millions, $ 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
Operating Revenues
Total operating revenues	$ 2,532	$ 3,952	$ 2,638	$ 3,229	$ 3,011	$ 4,434	$ 3,400	$ 3,829	$ 12,351	$ 14,674	$ 15,868
Operating Costs and Expenses
Cost of operations									8,555	10,784	11,808
Depreciation and amortization									1,367	1,566	1,523
Impairment losses									918	5,030	97
Selling, general and administrative									1,101	1,199	1,016
Acquisition-related transaction and integration costs									8	10	84
Research and Development Expense									90	146	88
Total operating costs and expenses									12,039	18,735	14,616
Gain on sale of assets									215	0	19
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments									0	21	0
Operating Income/(Loss)	(791)	755	87	476	(4,727)	379	232	76	527	(4,040)	1,271
Other Income/(Expense)
Equity in earnings of unconsolidated affiliates									27	36	38
Impairment losses on investments									(268)	(56)	0
Other income, net									42	33	22
(Loss)/gain on sale of equity method investment									0	(14)	18
Gain (Loss) on Extinguishment of Debt									(142)	75	(95)
Interest expense									(1,061)	(1,128)	(1,119)
Total other expense									(1,402)	(1,054)	(1,136)
(Loss)/Income Before Income Taxes									(875)	(5,094)	135
Income tax expense									16	1,342	3
Net (Loss)/Income	(1,055)	393	(276)	47	(6,358)	67	(9)	(136)	(891)	(6,436)	132
Less: Net loss attributable to noncontrolling interests and redeemable noncontrolling interests	(68)	(9)	(5)	(35)	(44)	1	5	(16)	(117)	(54)	(2)
Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest											17
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
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
(Loss)/Earnings Per Share Attributable to NRG Energy, Inc. Common Stockholders
Weighted average number of common shares outstanding — basic	316	316	315	315	315	331	333	336	316	329	334
Net (Loss)/Income per Weighted Average Common Share — Basic	$ (3.13)	$ 1.27	$ (0.61)	$ 0.24	$ (20.08)	$ 0.18	$ (0.06)	$ 0.37	$ (2.22)	$ (19.46)	$ 0.23
Weighted average number of common shares outstanding — diluted	316	317	315	315	315	332	333	336	316	329	339
Net (Loss)/Income per Weighted Average Common Share — Diluted	$ (3.13)	$ 1.27	$ (0.61)	$ 0.24	$ (20.08)	$ 0.18	$ (0.06)	$ (0.37)	$ (2.22)	$ (19.46)	$ 0.23
Dividends Per Common Share									$ 0.24	$ 0.58	$ 0.54