Condensed Consolidating Financial Information (Statements of Operations) (Details 2) - 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
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 transactions and integration costs										8		10		84
Research and Development Expense										90		146		88
Total operating costs and expenses										12,039		18,735		14,616
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal										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/(losses) of consolidated subsidiaries										0		0		0
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
Loss on debt extinguishment										(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 (loss)/income attributable to NRG Energy, Inc.		$ (987)	$ 402	$ (271)	$ 82	$ (6,314)	$ 66	$ (14)	$ (120)	(774)		(6,382)		134
Guarantor Subsidiaries
Operating Revenues
Total operating revenues										7,509		10,024		9,974
Operating Costs and Expenses
Cost of operations										5,402		7,712		7,909
Depreciation and amortization										565		787		801
Impairment losses										378		4,655		0
Selling, general and administrative										415		467		333
Acquisition related transactions and integration costs										0		1		3
Research and Development Expense										0		0		0
Total operating costs and expenses										6,760		13,622		9,046
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal										0				0
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments												0
Operating Income (Loss)										749		(3,598)		928
Other Income/(Expense)
Equity in earnings/(losses) of consolidated subsidiaries										(148)		(86)		317
Equity in earnings of unconsolidated affiliates										5		8		13
Impairment losses on investments										0		0
Other income, net										4		4		7
(Loss)/gain on sale of equity method investment												0		0
Loss on debt extinguishment										0		0		0
Interest expense										(15)		(18)		(19)
Total other expense										(154)		(92)		318
(Loss)/income before income taxes										595		(3,690)		1,246
Income tax expense										(1)		(1,104)		322
Net (Loss)/Income										596		(2,586)		924
Less: Net loss attributable to noncontrolling interests and redeemable noncontrolling interests										0		0		0
Net (loss)/income attributable to NRG Energy, Inc.										596		(2,586)		924
Non-Guarantor Subsidiaries
Operating Revenues
Total operating revenues										5,082		4,768		6,287
Operating Costs and Expenses
Cost of operations										3,355		3,176		4,220
Depreciation and amortization										776		759		706
Impairment losses										540		375		119
Selling, general and administrative										397		382		379
Acquisition related transactions and integration costs										1		(5)		15
Research and Development Expense										60		53		32
Total operating costs and expenses										5,129		4,740		5,471
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal										294				19
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments												(21)
Operating Income (Loss)										247		49		835
Other Income/(Expense)
Equity in earnings/(losses) of consolidated subsidiaries										(58)		(29)		219
Equity in earnings of unconsolidated affiliates										37		37		33
Impairment losses on investments										(268)		(25)
Other income, net										46		29		14
(Loss)/gain on sale of equity method investment												0		18
Loss on debt extinguishment										(4)		56		(9)
Interest expense										(574)		(564)		(525)
Total other expense										(821)		(496)		(250)
(Loss)/income before income taxes										(574)		(447)		585
Income tax expense										18		(96)		159
Net (Loss)/Income										(592)		(351)		426
Less: Net loss attributable to noncontrolling interests and redeemable noncontrolling interests										(103)		(23)		57
Net (loss)/income attributable to NRG Energy, Inc.										(489)		(328)		369
NRG Energy, Inc.
Operating Revenues
Total operating revenues										0		0		0
Operating Costs and Expenses
Cost of operations										42		14		4
Depreciation and amortization										26		20		16
Impairment losses										0		0		0
Selling, general and administrative										289		350		304
Acquisition related transactions and integration costs										7		14		66
Research and Development Expense										30		93		56
Total operating costs and expenses										394		491		446
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal										(79)				0
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments												0
Operating Income (Loss)										(473)		(491)		(446)
Other Income/(Expense)
Equity in earnings/(losses) of consolidated subsidiaries										313		(2,799)		775
Equity in earnings of unconsolidated affiliates										(5)		0		0
Impairment losses on investments										0		(31)
Other income, net										(6)		0		3
(Loss)/gain on sale of equity method investment												(14)		0
Loss on debt extinguishment										(138)		19		(86)
Interest expense										(472)		(546)		(575)
Total other expense										(308)		(3,371)		117
(Loss)/income before income taxes										(781)		(3,862)		(329)
Income tax expense										(63)		2,489		(478)
Net (Loss)/Income										(718)		(6,351)		149
Less: Net loss attributable to noncontrolling interests and redeemable noncontrolling interests										56		31		15
Net (loss)/income attributable to NRG Energy, Inc.										(774)		(6,382)		134
Consolidation, Eliminations [Member]
Operating Revenues
Total operating revenues										(240)	[1]	(118)	[2]	(393)	[3]
Operating Costs and Expenses
Cost of operations										(244)	[1]	(118)	[2]	(325)	[3]
Depreciation and amortization										0	[1],[4]	0	[2],[5]	0	[3],[6]
Impairment losses										0	[1]	0	[2]	(22)	[3]
Selling, general and administrative										0	[1]	0	[2]	0	[3]
Acquisition related transactions and integration costs										0	[1]	0	[2]	0	[3]
Research and Development Expense										0	[1]	0	[2]	0	[3]
Total operating costs and expenses										(244)	[1]	(118)	[2]	(347)	[3]
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal										0	[1]			0	[3]
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments	[2],[5]											0
Operating Income (Loss)										4	[1]	0	[2]	(46)	[3]
Other Income/(Expense)
Equity in earnings/(losses) of consolidated subsidiaries										(107)	[1]	2,914	[2]	(1,311)	[3]
Equity in earnings of unconsolidated affiliates										(10)	[1],[4]	(9)	[2],[5]	(8)	[3],[6]
Impairment losses on investments										0	[1]	0	[2]
Other income, net										(2)	[1]	0	[2]	(2)	[3]
(Loss)/gain on sale of equity method investment												0	[2]	0	[3]
Loss on debt extinguishment										0	[1]	0	[2]	0	[3]
Interest expense										0	[1]	0	[2]	0	[3]
Total other expense										(119)	[1]	2,905	[2]	(1,321)	[3]
(Loss)/income before income taxes										(115)	[1]	2,905	[2]	(1,367)	[3]
Income tax expense										62	[1]	53	[2]	0	[3]
Net (Loss)/Income										(177)	[1],[4]	2,852	[2],[5]	(1,367)	[3],[6]
Less: Net loss attributable to noncontrolling interests and redeemable noncontrolling interests										(70)	[1]	(62)	[2]	(74)	[3]
Net (loss)/income attributable to NRG Energy, Inc.										$ (107)	[1]	$ 2,914	[2]	$ (1,293)	[3]

[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.