Condensed Consolidating Financial Information (Statements of Comprehensive Income) (Details 3) - 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
Unrealized gain on derivatives, net										35		(15)		(45)
Foreign currency translation adjustments, net										(1)		(11)		(8)
Available-for-sale securities, net										1		17		(7)
Defined benefit plan, net										3		10		(129)
Other comprehensive income/(loss)										38		1		(189)
Comprehensive income/(loss)										(853)		(6,435)		(57)
Less: Comprehensive income/(loss) attributable to noncontrolling interest										(117)		(73)		8
Comprehensive income/(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)/income, Net of Tax, Available for Common Stockholders										(663)		(6,382)		(121)
Guarantor Subsidiaries
Net (Loss)/Income										596		(2,586)		924
Unrealized gain on derivatives, net										0		(9)		(49)
Foreign currency translation adjustments, net										(1)		0		0
Available-for-sale securities, net										0		0		0
Defined benefit plan, net										36		22		5
Other comprehensive income/(loss)										35		(31)		(44)
Comprehensive income/(loss)										631		(2,617)		880
Less: Comprehensive income/(loss) attributable to noncontrolling interest										0		0		0
Comprehensive income/(loss) attributable to NRG Energy, Inc.										631		(2,617)		880
Preferred Stock Dividends, Income Statement Impact										0		0		0
Gain on Redemption of Redeemable Preferred Stock										0
Comprehensive (loss)/income, Net of Tax, Available for Common Stockholders										631		(2,617)		880
Non-Guarantor Subsidiaries
Net (Loss)/Income										(592)		(351)		426
Unrealized gain on derivatives, net										32		(13)		(89)
Foreign currency translation adjustments, net										(1)		(7)		(12)
Available-for-sale securities, net										0		(1)		1
Defined benefit plan, net										(23)		15		(104)
Other comprehensive income/(loss)										8		(36)		(204)
Comprehensive income/(loss)										(584)		(387)		222
Less: Comprehensive income/(loss) attributable to noncontrolling interest										(103)		(42)		67
Comprehensive income/(loss) attributable to NRG Energy, Inc.										(481)		(345)		155
Preferred Stock Dividends, Income Statement Impact										0		0		0
Gain on Redemption of Redeemable Preferred Stock										0
Comprehensive (loss)/income, Net of Tax, Available for Common Stockholders										(481)		(345)		155
NRG Energy, Inc.
Net (Loss)/Income										(718)		(6,351)		149
Unrealized gain on derivatives, net										89		48		(215)
Foreign currency translation adjustments, net										(1)		(4)		4
Available-for-sale securities, net										1		18		(8)
Defined benefit plan, net										(51)		42		20
Other comprehensive income/(loss)										38		20		(199)
Comprehensive income/(loss)										(680)		(6,331)		(50)
Less: Comprehensive income/(loss) attributable to noncontrolling interest										56		31		15
Comprehensive income/(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)
Comprehensive (loss)/income, Net of Tax, Available for Common Stockholders										(663)		(6,382)		(121)
Consolidation, Eliminations [Member]
Net (Loss)/Income										(177)	[1],[2]	2,852	[3],[4]	(1,367)	[5],[6]
Unrealized gain on derivatives, net										(86)	[7]	(41)	[8]	308	[9]
Foreign currency translation adjustments, net										2	[7]	0	[8]	0	[9]
Available-for-sale securities, net										0	[7]	0	[8]	0	[9]
Defined benefit plan, net										41	[7]	(89)	[8]	(50)	[9]
Other comprehensive income/(loss)										(43)	[7]	48	[8]	258	[9]
Comprehensive income/(loss)										(220)	[7]	2,900	[8]	(1,109)	[9]
Less: Comprehensive income/(loss) attributable to noncontrolling interest										(70)	[7]	(62)	[8]	(74)	[9]
Comprehensive income/(loss) attributable to NRG Energy, Inc.										(150)	[7]	2,962	[8]	(1,035)	[9]
Preferred Stock Dividends, Income Statement Impact										0	[7]	0	[8]	0	[9]
Gain on Redemption of Redeemable Preferred Stock	[7]									0
Comprehensive (loss)/income, Net of Tax, Available for Common Stockholders										$ (150)	[7]	$ 2,962	[8]	$ (1,035)	[9]

[1] All significant intercompany transactions have been eliminated in consolidation.

[2] All significant intercompany transactions have been eliminated in consolidation.

[3] All significant intercompany transactions have been eliminated in consolidation.

[4] All significant intercompany transactions have been eliminated in consolidation.

[5] All significant intercompany transactions have been eliminated in consolidation.

[6] All significant intercompany transactions have been eliminated in consolidation.

[7] All significant intercompany transactions have been eliminated in consolidation.

[8] All significant intercompany transactions have been eliminated in consolidation.

[9] All significant intercompany transactions have been eliminated in consolidation.