Segment Reporting (Details)	3 Months Ended										12 Months Ended
	Dec. 31, 2015 USD ($)		Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)		Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) customer		Dec. 31, 2014 USD ($) customer		Dec. 31, 2013 USD ($) customer		Nov. 02, 2015 USD ($)
Income Statement
Operating revenues	$ 3,011,000,000		$ 4,434,000,000	$ 3,400,000,000	$ 3,829,000,000	$ 4,192,000,000		$ 4,569,000,000	$ 3,621,000,000	$ 3,486,000,000	$ 14,674,000,000	[1]	$ 15,868,000,000	[2]	$ 11,295,000,000	[3]
Operating expenses											11,975,000,000		12,821,000,000		9,025,000,000
Depreciation and amortization											1,566,000,000		1,523,000,000		1,256,000,000
Impairment of Long-Lived Assets Held-for-use											5,030,000,000		97,000,000		459,000,000
Acquisition-related transaction and integration costs											10,000,000		84,000,000		128,000,000
Research and Development Expense											154,000,000		91,000,000		84,000,000
Costs and Expenses											18,735,000,000		14,616,000,000		10,952,000,000
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal											21,000,000		19,000,000		0
Operating Income (Loss)	(4,727,000,000)		379,000,000	232,000,000	76,000,000	453,000,000		549,000,000	89,000,000	180,000,000	(4,040,000,000)		1,271,000,000		343,000,000
Equity in earnings/(losses) of unconsolidated affiliates											36,000,000		38,000,000		7,000,000
Impairment losses on investments											(56,000,000)		0		(99,000,000)
Other income, net											33,000,000		22,000,000		13,000,000
(Loss)/gain on sale of equity-method investment											(14,000,000)		18,000,000		0
Net gain/(loss) on debt extinguishment											75,000,000		(95,000,000)		(50,000,000)
Interest expense											(1,128,000,000)		(1,119,000,000)		(848,000,000)
Income/(loss) before income taxes											(5,094,000,000)		135,000,000		(634,000,000)
Income tax expense/(benefit)											1,342,000,000		3,000,000		(282,000,000)
Net (Loss)/Income	(6,358,000,000)		67,000,000	(9,000,000)	(136,000,000)	97,000,000		182,000,000	(80,000,000)	(67,000,000)	(6,436,000,000)		132,000,000		(352,000,000)
Less: Net (loss)/income attributable to noncontrolling interests and redeemable noncontrolling interests	(44,000,000)		1,000,000	5,000,000	(16,000,000)	(22,000,000)		14,000,000	17,000,000	(11,000,000)	(54,000,000)		(2,000,000)		34,000,000
Net (loss)/income attributable to NRG Energy, Inc.	(6,314,000,000)		$ 66,000,000	$ (14,000,000)	$ (120,000,000)	119,000,000		$ 168,000,000	$ (97,000,000)	$ (56,000,000)	(6,382,000,000)		134,000,000		(386,000,000)
Operating revenues include inter-segment sales and net derivative gains and losses of:											1,218,000,000		1,949,000,000		2,308,000,000
Balance sheet
Equity investments in affiliates	1,045,000,000					771,000,000					1,045,000,000		771,000,000
Capital expenditures	1,267,000,000	[4]				984,000,000	[5]				1,267,000,000	[4]	984,000,000	[5]
Goodwill	999,000,000					2,574,000,000					999,000,000		2,574,000,000
Total assets	32,882,000,000					40,466,000,000					32,882,000,000		40,466,000,000
Retail
Income Statement
Operating revenues											9,142,000,000	[1]	11,024,000,000	[2]	8,638,000,000	[3]
Operating expenses											7,811,000,000		8,894,000,000		7,235,000,000
Depreciation and amortization											907,000,000		966,000,000		930,000,000
Impairment of Long-Lived Assets Held-for-use											4,827,000,000		87,000,000		459,000,000
Acquisition-related transaction and integration costs											0		1,000,000		0
Research and Development Expense											24,000,000		13,000,000		14,000,000
Costs and Expenses											13,569,000,000		9,961,000,000		8,638,000,000
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal											21,000,000		19,000,000
Operating Income (Loss)											(4,406,000,000)		1,082,000,000		0
Equity in earnings/(losses) of unconsolidated affiliates											7,000,000		23,000,000		(6,000,000)
Impairment losses on investments											14,000,000				0
Other income, net											40,000,000		35,000,000		32,000,000
(Loss)/gain on sale of equity-method investment											0		18,000,000
Net gain/(loss) on debt extinguishment											0		0		0
Interest expense											98,000,000		95,000,000		107,000,000
Income/(loss) before income taxes											(4,471,000,000)		1,063,000,000		(81,000,000)
Income tax expense/(benefit)											1,000,000		1,000,000		0
Net (Loss)/Income											(4,472,000,000)		1,062,000,000		(81,000,000)
Less: Net (loss)/income attributable to noncontrolling interests and redeemable noncontrolling interests											0		(1,000,000)		0
Net (loss)/income attributable to NRG Energy, Inc.											(4,472,000,000)		1,063,000,000		(81,000,000)
Operating revenues include inter-segment sales and net derivative gains and losses of:											947,000,000		1,820,000,000		2,055,000,000
Balance sheet
Equity investments in affiliates	185,000,000					141,000,000					185,000,000		141,000,000
Capital expenditures	798,000,000	[4]				611,000,000	[5]				798,000,000	[4]	611,000,000	[5]
Goodwill	536,000,000					1,746,000,000					536,000,000		1,746,000,000
Total assets	$ 17,139,000,000					28,317,000,000					17,139,000,000		28,317,000,000
NRG Home Retail [Member]
Income Statement
Operating revenues											5,389,000,000	[1]	5,503,000,000	[2]	4,341,000,000	[3]
Operating expenses											4,577,000,000		5,240,000,000		3,814,000,000
Depreciation and amortization											123,000,000		122,000,000		141,000,000
Impairment of Long-Lived Assets Held-for-use											36,000,000		0		0
Acquisition-related transaction and integration costs											1,000,000		3,000,000		0
Research and Development Expense											0		0		0
Costs and Expenses											4,737,000,000		5,365,000,000		3,955,000,000
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal											0		0
Operating Income (Loss)											652,000,000		138,000,000		386,000,000
Equity in earnings/(losses) of unconsolidated affiliates											0		0		0
Impairment losses on investments											0				0
Other income, net											0		0		0
(Loss)/gain on sale of equity-method investment											0		0
Net gain/(loss) on debt extinguishment											0		0		0
Interest expense											0		1,000,000		2,000,000
Income/(loss) before income taxes											652,000,000		137,000,000		384,000,000
Income tax expense/(benefit)											0		0		0
Net (Loss)/Income											652,000,000		137,000,000		384,000,000
Less: Net (loss)/income attributable to noncontrolling interests and redeemable noncontrolling interests											0		0		0
Net (loss)/income attributable to NRG Energy, Inc.											652,000,000		137,000,000		384,000,000
Operating revenues include inter-segment sales and net derivative gains and losses of:											$ 6,000,000		7,000,000		5,000,000
Balance sheet
Equity investments in affiliates						0							0
Capital expenditures	$ 30,000,000	[4]				34,000,000	[5]				$ 30,000,000	[4]	34,000,000	[5]
Goodwill	340,000,000					387,000,000					340,000,000		387,000,000
Total assets	1,876,000,000					6,049,000,000					1,876,000,000		6,049,000,000
Home Solar [Member]
Income Statement
Operating revenues											32,000,000	[1]	42,000,000	[2]	4,000,000	[3]
Operating expenses											204,000,000		108,000,000		0
Depreciation and amortization											25,000,000		6,000,000		4,000,000
Impairment of Long-Lived Assets Held-for-use											132,000,000		0		0
Acquisition-related transaction and integration costs											(8,000,000)		0		0
Research and Development Expense											0		0		9,000,000
Costs and Expenses											353,000,000		114,000,000		13,000,000
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal											0		0
Operating Income (Loss)											(321,000,000)		(72,000,000)		(9,000,000)
Equity in earnings/(losses) of unconsolidated affiliates											0		0		0
Impairment losses on investments											0				0
Other income, net											0		0		0
(Loss)/gain on sale of equity-method investment											0		0
Net gain/(loss) on debt extinguishment											0		0		0
Interest expense											3,000,000		1,000,000		0
Income/(loss) before income taxes											(324,000,000)		(73,000,000)		(9,000,000)
Income tax expense/(benefit)											0		0		0
Net (Loss)/Income											(324,000,000)		(73,000,000)		(9,000,000)
Less: Net (loss)/income attributable to noncontrolling interests and redeemable noncontrolling interests											(20,000,000)		(19,000,000)		0
Net (loss)/income attributable to NRG Energy, Inc.											(304,000,000)		(54,000,000)		(9,000,000)
Operating revenues include inter-segment sales and net derivative gains and losses of:											1,000,000		0		0
Balance sheet
Equity investments in affiliates	0					0					0		0
Capital expenditures	144,000,000	[4]				113,000,000	[5]				144,000,000	[4]	113,000,000	[5]
Goodwill	0					98,000,000					0		98,000,000
Total assets	413,000,000					222,000,000					413,000,000		222,000,000
NRG Renew [Member]
Income Statement
Operating revenues											474,000,000	[1]	427,000,000	[2],[6]	214,000,000	[3]
Operating expenses											218,000,000		183,000,000	[6]	77,000,000
Depreciation and amortization											212,000,000		195,000,000	[6]	86,000,000
Impairment of Long-Lived Assets Held-for-use											13,000,000		32,000,000	[6]	0
Acquisition-related transaction and integration costs											0		0	[6]	0
Research and Development Expense											70,000,000		42,000,000	[6]	34,000,000
Costs and Expenses											513,000,000		452,000,000	[6]	197,000,000
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal											0		0	[6]
Operating Income (Loss)											(39,000,000)		(25,000,000)	[6]	17,000,000
Equity in earnings/(losses) of unconsolidated affiliates											$ 1,000,000		(4,000,000)	[6]	(7,000,000)
Impairment losses on investments															0
Other income, net											$ 4,000,000		5,000,000	[6]	2,000,000
(Loss)/gain on sale of equity-method investment											0		0	[6]
Net gain/(loss) on debt extinguishment											0		(1,000,000)	[6]	0
Interest expense											108,000,000		122,000,000	[6]	52,000,000
Income/(loss) before income taxes											(142,000,000)		(147,000,000)	[6]	(40,000,000)
Income tax expense/(benefit)											(18,000,000)		0	[6]	0
Net (Loss)/Income											(124,000,000)		(147,000,000)	[6]	(40,000,000)
Less: Net (loss)/income attributable to noncontrolling interests and redeemable noncontrolling interests											6,000,000		2,000,000	[6]	22,000,000
Net (loss)/income attributable to NRG Energy, Inc.											(130,000,000)		(149,000,000)	[6]	(62,000,000)
Operating revenues include inter-segment sales and net derivative gains and losses of:											23,000,000		25,000,000		14,000,000
Balance sheet
Equity investments in affiliates	134,000,000					148,000,000	[6]				134,000,000		148,000,000	[6]
Capital expenditures	163,000,000	[4]				160,000,000	[5],[6]				163,000,000	[4]	160,000,000	[5],[6]
Goodwill	12,000,000					12,000,000	[6]				12,000,000		12,000,000	[6]
Total assets	5,954,000,000					6,481,000,000	[6]				5,954,000,000		6,481,000,000	[6]
NRG Yield
Income Statement
Operating revenues											869,000,000	[1]	746,000,000	[2]	387,000,000	[3]
Operating expenses											324,000,000		274,000,000		155,000,000
Depreciation and amortization											265,000,000		202,000,000		74,000,000
Impairment of Long-Lived Assets Held-for-use											0		0		0
Acquisition-related transaction and integration costs											3,000,000		4,000,000		0
Research and Development Expense											0		0		0
Costs and Expenses											592,000,000		480,000,000		229,000,000
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal											0		0
Operating Income (Loss)											277,000,000		266,000,000		158,000,000
Equity in earnings/(losses) of unconsolidated affiliates											35,000,000		25,000,000		22,000,000
Impairment losses on investments											0				0
Other income, net											2,000,000		3,000,000		3,000,000
(Loss)/gain on sale of equity-method investment											0		0
Net gain/(loss) on debt extinguishment											(9,000,000)		0		0
Interest expense											238,000,000		191,000,000		52,000,000
Income/(loss) before income taxes											67,000,000		103,000,000		131,000,000
Income tax expense/(benefit)											12,000,000		4,000,000		8,000,000
Net (Loss)/Income											55,000,000		99,000,000		123,000,000
Less: Net (loss)/income attributable to noncontrolling interests and redeemable noncontrolling interests											19,000,000		16,000,000		13,000,000
Net (loss)/income attributable to NRG Energy, Inc.											36,000,000		83,000,000		110,000,000
Operating revenues include inter-segment sales and net derivative gains and losses of:											29,000,000		12,000,000		7,000,000
Balance sheet
Equity investments in affiliates	798,000,000					410,000,000					798,000,000		410,000,000
Capital expenditures	30,000,000	[4]				13,000,000	[5]				30,000,000	[4]	13,000,000	[5]
Goodwill	0					0					0		0
Total assets	7,775,000,000					7,860,000,000					7,775,000,000		7,860,000,000
Corporate
Income Statement
Operating revenues											(14,000,000)	[1]	75,000,000	[2]	19,000,000	[3]
Operating expenses											61,000,000		72,000,000		41,000,000
Depreciation and amortization											34,000,000		32,000,000		21,000,000
Impairment of Long-Lived Assets Held-for-use											0		0		0
Acquisition-related transaction and integration costs											14,000,000		76,000,000		128,000,000
Research and Development Expense											60,000,000		36,000,000		27,000,000
Costs and Expenses											169,000,000		216,000,000		217,000,000
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal											0		0
Operating Income (Loss)											(183,000,000)		(141,000,000)		(198,000,000)
Equity in earnings/(losses) of unconsolidated affiliates											0		3,000,000		0
Impairment losses on investments											42,000,000				99,000,000
Other income, net											84,000,000		78,000,000		77,000,000
(Loss)/gain on sale of equity-method investment											(14,000,000)		0
Net gain/(loss) on debt extinguishment											84,000,000		(94,000,000)		(50,000,000)
Interest expense											776,000,000		806,000,000		735,000,000
Income/(loss) before income taxes											(847,000,000)		(960,000,000)		(1,005,000,000)
Income tax expense/(benefit)											1,347,000,000		(2,000,000)		(290,000,000)
Net (Loss)/Income											(2,194,000,000)		(958,000,000)		(715,000,000)
Less: Net (loss)/income attributable to noncontrolling interests and redeemable noncontrolling interests											(17,000,000)		24,000,000		14,000,000
Net (loss)/income attributable to NRG Energy, Inc.											(2,177,000,000)		(982,000,000)		(729,000,000)
Operating revenues include inter-segment sales and net derivative gains and losses of:											212,000,000		85,000,000		227,000,000
Balance sheet
Equity investments in affiliates	276,000,000					174,000,000					276,000,000		174,000,000
Capital expenditures	102,000,000	[4]				53,000,000	[5]				102,000,000	[4]	53,000,000	[5]
Goodwill	111,000,000					331,000,000					111,000,000		331,000,000
Total assets	19,576,000,000					30,727,000,000					19,576,000,000		30,727,000,000
Eliminations
Income Statement
Operating revenues											(1,218,000,000)	[1]	(1,949,000,000)	[2],[6]	(2,308,000,000)	[3]
Operating expenses											(1,220,000,000)		(1,950,000,000)	[6]	(2,297,000,000)
Depreciation and amortization											0		0	[6]	0
Impairment of Long-Lived Assets Held-for-use											22,000,000		(22,000,000)	[6]	0
Acquisition-related transaction and integration costs											0		0	[6]	0
Research and Development Expense											0		0	[6]	0
Costs and Expenses											(1,198,000,000)		(1,972,000,000)	[6]	(2,297,000,000)
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal											0		0	[6]
Operating Income (Loss)											(20,000,000)		23,000,000	[6]	(11,000,000)
Equity in earnings/(losses) of unconsolidated affiliates											(7,000,000)		(9,000,000)	[6]	(2,000,000)
Impairment losses on investments											0				0
Other income, net											(97,000,000)		(99,000,000)	[6]	(101,000,000)
(Loss)/gain on sale of equity-method investment											0		0	[6]
Net gain/(loss) on debt extinguishment											0		0	[6]	0
Interest expense											(95,000,000)		(97,000,000)	[6]	(100,000,000)
Income/(loss) before income taxes											(29,000,000)		12,000,000	[6]	(14,000,000)
Income tax expense/(benefit)											0		0	[6]	0
Net (Loss)/Income											(29,000,000)		12,000,000	[6]	(14,000,000)
Less: Net (loss)/income attributable to noncontrolling interests and redeemable noncontrolling interests											(42,000,000)		(24,000,000)	[6]	(15,000,000)
Net (loss)/income attributable to NRG Energy, Inc.											13,000,000		36,000,000	[6]	1,000,000
Operating revenues include inter-segment sales and net derivative gains and losses of:											0		0		$ 0
Balance sheet
Equity investments in affiliates	(348,000,000)					(102,000,000)	[6]				(348,000,000)		(102,000,000)	[6]
Capital expenditures	0	[4]				0	[5],[6]				0	[4]	0	[5],[6]
Goodwill	0					0	[6]				0		0	[6]
Total assets	$ (19,851,000,000)					$ (39,190,000,000)	[6]				$ (19,851,000,000)		$ (39,190,000,000)	[6]
Customers
Segment Reporting Information
Concentration Risk, Number of Customers Accouting for More Than Ten Percent of Revenues | customer											0		0		0
Threshold percentage of the Company's consolidated revenues attributable to a customer											10.00%		10.00%		10.00%
ROFO Assets [Member]
Segment Reporting Information
Percentage of Ownership Sold of Subsidiary																	75.00%
Balance sheet
Number of Facilities																	12

[1] (a) Operating revenues include inter-segment sales and net derivative gains and losses of:$947 $6 $1 $23 $29 $212 $— $1,218

[2] (c) Operating revenues include inter-segment sales and net derivative gains and losses of:$1,820 $7 $— $25 $12 $85 $— $1,949

[3] (f) Operating revenues include inter-segment sales and net derivative gains and losses of:$2,055 $5 $— $14 $7 $227 $— $2,308

[4] Includes accruals

[5] Includes accruals.

[6] Includes an impairment loss resulting from the intercompany sale of solar panels at current market rates. The use of these long-lived assets is anticipated to generate sufficient cash flows to recover the historical cost of the assets and accordingly, the impairment loss was eliminated and the assets remain at historical cost in consolidation.