Debt and Capital Leases (Details) (USD $)	3 Months Ended		9 Months Ended			3 Months Ended								9 Months Ended													0 Months Ended	3 Months Ended			9 Months Ended		12 Months Ended								9 Months Ended					9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended		12 Months Ended		9 Months Ended	12 Months Ended	9 Months Ended		12 Months Ended										9 Months Ended	12 Months Ended	2 Months Ended	9 Months Ended		9 Months Ended		12 Months Ended										9 Months Ended		12 Months Ended		9 Months Ended		12 Months Ended		3 Months Ended	9 Months Ended		12 Months Ended		9 Months Ended		12 Months Ended		3 Months Ended		12 Months Ended			9 Months Ended	12 Months Ended		9 Months Ended			1 Months Ended					3 Months Ended							9 Months Ended					0 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 Interest Rate Swap [Member] NRG Peaker Finance Co. LLC, bonds, due 2019	Sep. 30, 2012 Interest Rate Swap [Member] Solar Power Partners - SPP Fund II [Member]	Sep. 30, 2012 Interest Rate Swap [Member] Solar Power Partners - SPP Fund II-B [Member]	Sep. 30, 2012 Interest Rate Swap [Member] Solar Power Partners III [Member]	Sep. 30, 2012 Recourse Debt [Member]	Dec. 31, 2011 Recourse Debt [Member]	Sep. 30, 2012 Non Recourse Debt [Member]	Dec. 31, 2011 Non Recourse Debt [Member]	Sep. 30, 2012 Senior Notes Due in 2023 [Member] day	Sep. 30, 2012 Senior Notes Due in 2023 [Member] Recourse Debt [Member]	Dec. 31, 2011 Senior Notes Due in 2023 [Member] Recourse Debt [Member]	Sep. 30, 2012 7.875% Senior notes, due 2021 Recourse Debt [Member]	Dec. 31, 2011 7.875% Senior notes, due 2021 Recourse Debt [Member]	Sep. 30, 2012 Senior Notes Due In 2020 [Member] Recourse Debt [Member]	Dec. 31, 2011 Senior Notes Due In 2020 [Member] Recourse Debt [Member]	Sep. 30, 2012 7.625% Senior notes, due 2019 Recourse Debt [Member]	Dec. 31, 2011 7.625% Senior notes, due 2019 Recourse Debt [Member]	Sep. 30, 2012 8.50% Senior notes, due 2019 Recourse Debt [Member]	Dec. 31, 2011 8.50% Senior notes, due 2019 Recourse Debt [Member]	Sep. 30, 2012 7.625% Senior notes, due 2018 Recourse Debt [Member]	Dec. 31, 2011 7.625% Senior notes, due 2018 Recourse Debt [Member]	Oct. 24, 2012 7.375% Senior notes, due 2017	Sep. 30, 2012 7.375% Senior notes, due 2017	Sep. 30, 2012 7.375% Senior notes, due 2017 Recourse Debt [Member]	Dec. 31, 2011 7.375% Senior notes, due 2017 Recourse Debt [Member]	Sep. 30, 2012 Senior Credit Facility Due 2018 [Member] Recourse Debt [Member]		Dec. 31, 2011 Senior Credit Facility Due 2018 [Member] Recourse Debt [Member]		Sep. 30, 2012 Indian River Power LLC, tax-exempt bonds, due 2040 Recourse Debt [Member]	Dec. 31, 2011 Indian River Power LLC, tax-exempt bonds, due 2040 Recourse Debt [Member]	Sep. 30, 2012 Indian River Power LLC, tax-exempt bonds, due 2045 Recourse Debt [Member]	Dec. 31, 2011 Indian River Power LLC, tax-exempt bonds, due 2045 Recourse Debt [Member]	Sep. 30, 2012 Dunkirk Power LLC, tax-exempt bonds, due 2042 Recourse Debt [Member]	Dec. 31, 2011 Dunkirk Power LLC, tax-exempt bonds, due 2042 Recourse Debt [Member]	Sep. 30, 2012 Fort Bend County Industrial Development Corporation - Loan Agreement [Member]	Oct. 18, 2012 Fort Bend County Industrial Development Corporation - Loan Agreement [Member]	May 03, 2012 Fort Bend County Industrial Development Corporation - Loan Agreement [Member]	Sep. 30, 2012 Fort Bend County Industrial Development Corporation - Loan Agreement [Member] Recourse Debt [Member]	Dec. 31, 2011 Fort Bend County Industrial Development Corporation - Loan Agreement [Member] Recourse Debt [Member]	Sep. 30, 2012 Fort Bend County Industrial Development Corporation - Loan Agreement [Member] Non Recourse Debt [Member]	Dec. 31, 2011 Fort Bend County Industrial Development Corporation - Loan Agreement [Member] Non Recourse Debt [Member]	Sep. 30, 2012 Solar Partners I, due 2014 and 2033 Non Recourse Debt [Member]	Dec. 31, 2011 Solar Partners I, due 2014 and 2033 Non Recourse Debt [Member]	Sep. 30, 2012 Solar Partners II, due 2014 and 2038 Non Recourse Debt [Member]	Dec. 31, 2011 Solar Partners II, due 2014 and 2038 Non Recourse Debt [Member]	Sep. 30, 2012 Solar Partners VIII, due 2014 and 2038 Non Recourse Debt [Member]	Dec. 31, 2011 Solar Partners VIII, due 2014 and 2038 Non Recourse Debt [Member]	Sep. 30, 2012 NRG Peaker Finance Co. LLC, bonds, due 2019 Non Recourse Debt [Member]		Dec. 31, 2011 NRG Peaker Finance Co. LLC, bonds, due 2019 Non Recourse Debt [Member]		Sep. 30, 2012 Agua Caliente Financing Agreement [Member] Non Recourse Debt [Member]	Dec. 31, 2011 Agua Caliente Financing Agreement [Member] Non Recourse Debt [Member]	Sep. 30, 2012 West Holdings Credit Agreement [Member] Non Recourse Debt [Member]		Dec. 31, 2011 West Holdings Credit Agreement [Member] Non Recourse Debt [Member]		Sep. 30, 2012 West Holdings Credit Agreement [Member] Non Recourse Debt [Member] Minimum [Member]		Dec. 31, 2011 West Holdings Credit Agreement [Member] Non Recourse Debt [Member] Minimum [Member]		Sep. 30, 2012 West Holdings Credit Agreement [Member] Non Recourse Debt [Member] Maximum [Member]		Dec. 31, 2011 West Holdings Credit Agreement [Member] Non Recourse Debt [Member] Maximum [Member]		Sep. 30, 2012 NRG Energy Center Minneapolis LLC, senior secured notes, due 2013, 2017, and 2025 Non Recourse Debt [Member]	Dec. 31, 2011 NRG Energy Center Minneapolis LLC, senior secured notes, due 2013, 2017, and 2025 Non Recourse Debt [Member]	Mar. 09, 2012 CVSR Financing Agreement [Member] Non Recourse Debt [Member]	Sep. 30, 2012 CVSR Financing Agreement [Member] Non Recourse Debt [Member]	Dec. 31, 2011 CVSR Financing Agreement [Member] Non Recourse Debt [Member]	Sep. 30, 2012 South Trent Wind LLC, financing agreement, due 2020 Non Recourse Debt [Member]		Dec. 31, 2011 South Trent Wind LLC, financing agreement, due 2020 Non Recourse Debt [Member]		Sep. 30, 2012 South Trent Wind LLC, financing agreement, due 2020 Non Recourse Debt [Member] Minimum [Member]		Dec. 31, 2011 South Trent Wind LLC, financing agreement, due 2020 Non Recourse Debt [Member] Minimum [Member]		Sep. 30, 2012 South Trent Wind LLC, financing agreement, due 2020 Non Recourse Debt [Member] Maximum [Member]		Dec. 31, 2011 South Trent Wind LLC, financing agreement, due 2020 Non Recourse Debt [Member] Maximum [Member]		Sep. 30, 2012 Solar Power Partners - SPP Fund II/II-B [Member] Non Recourse Debt [Member]		Dec. 31, 2011 Solar Power Partners - SPP Fund II/II-B [Member] Non Recourse Debt [Member]		Sep. 30, 2012 Solar Power Partners - SPP Fund III [Member] Non Recourse Debt [Member]		Dec. 31, 2011 Solar Power Partners - SPP Fund III [Member] Non Recourse Debt [Member]		Mar. 20, 2012 Roadrunner Financing Agreement	Sep. 30, 2012 Roadrunner Financing Agreement Non Recourse Debt [Member]		Dec. 31, 2011 Roadrunner Financing Agreement Non Recourse Debt [Member]		Sep. 30, 2012 NRG Solar Blythe LLC, credit agreement, due 2028 Non Recourse Debt [Member]		Dec. 31, 2011 NRG Solar Blythe LLC, credit agreement, due 2028 Non Recourse Debt [Member]		Sep. 30, 2012 Avra Valley Financing Agreement [Member]	Aug. 30, 2012 Avra Valley Financing Agreement [Member]	Dec. 31, 2011 Avra Valley Financing Agreement [Member] Non Recourse Debt [Member]	Sep. 30, 2012 Avra Valley Financing Agreement [Member] Non Recourse Debt [Member]	Sep. 30, 2012 Avra Valley Financing Agreement [Member] Bridge Loan [Member]	Sep. 30, 2012 Other Non Recourse Debt [Member]	Dec. 31, 2011 Other Non Recourse Debt [Member]	Sep. 30, 2012 Senior Notes [Member] Recourse Debt [Member]	Sep. 30, 2012 Senior Notes Due in 2023 6625 [Member]	Sep. 24, 2012 Senior Notes Due in 2023 6625 [Member]	Jan. 25, 2012 NRG Repowering Holdings LLC [Member]	Jan. 31, 2012 NRG Repowering Holdings LLC Working Capital Facility [Member]	Sep. 30, 2012 NRG Repowering Holdings LLC Working Capital Facility [Member]	Jan. 25, 2012 NRG Repowering Holdings LLC Working Capital Facility [Member]	Sep. 30, 2012 NRG Repowering Holdings LLC Credit Facility [Member]	Jan. 25, 2012 NRG Repowering Holdings LLC Credit Facility [Member]	Sep. 30, 2012 Alpine Financing Agreement	Mar. 16, 2012 Alpine Financing Agreement	Sep. 30, 2012 Alpine Financing Agreement Bridge Loan [Member]	Sep. 30, 2012 Alpine Financing Agreement Cash Grant Loan [Member]	Sep. 30, 2012 Alpine Financing Agreement Letter of Credit [Member]	Sep. 30, 2012 Schkopau Capital Lease [Member]	Dec. 31, 2011 Schkopau Capital Lease [Member]	Sep. 30, 2012 Redemption Period Prior To 15 September 2015 [Member] Senior Notes Due in 2023 [Member]	Sep. 30, 2012 Redemption Period From 15 September 2017 to 14 September 2018 [Member] Senior Notes Due in 2023 6625 [Member]	Sep. 30, 2012 Redemption Period From 15 September 1018 to 14 September 2019 [Member] Senior Notes Due in 2023 6625 [Member]	Sep. 30, 2012 Redemption Period From 15 September 2019 to 14 September 2020 [Member] Senior Notes Due in 2023 6625 [Member]	Sep. 30, 2012 Redemption Period Beginning With 15 September 2020 [Member] Senior Notes Due in 2023 6625 [Member]	Sep. 24, 2012 Redemption Part One [Member] 7.375% Senior notes, due 2017	Oct. 24, 2012 Redemption Part Two [Member] 7.375% Senior notes, due 2017	Sep. 24, 2012 Redemption Part Two [Member] 7.375% Senior notes, due 2017	Oct. 24, 2012 Redemption Part Three [Member] 7.375% Senior notes, due 2017
Long-term debt disclosure
Sale Energie GmbH, Schkopau capital lease, due 2021																																																																																																																															$ 0	$ 103,000,000
Subtotal	11,342,000,000		11,342,000,000		9,832,000,000
Less current maturities	374,000,000		374,000,000		87,000,000
Total long-term debt and capital leases	10,968,000,000		10,968,000,000		9,745,000,000
Long-term debt																																										73,000,000	54,000,000																																																																8,000,000								990,000,000								68,000,000
Interest rate															6.625%		7.875%		8.25%		7.625%		8.50%		7.625%				7.375%						6.00%		5.375%		5.875%			4.75%																																																																								6.625%							3.50%
Repayments of Senior Debt																																																																																																																																						820,000,000	0		270,000,000
Redemption Price Percentage of Face Amount																																																																																																																																						104.125%		101.125%	103.688%
Loss on debt extinguishment	(41,000,000)	(32,000,000)	(41,000,000)	(175,000,000)																							10,000,000	41,000,000
Proceeds from Issuance of Debt																																																																																																																		978,000,000
Maximum Redeemable Percentage Of Principal, Prior To Maturity																																																																																																																																	35.00%
Redemption Price As Percentage Of Principal Amount, Prior To Maturity																																																																																																																																	106.625%	103.313%	102.208%	101.104%	100.00%
Percentage of Face Amount, Senior Notes Paid as Premium on Redemption																																																																																																																																	1.00%
Percentage Of Principal Amount Used To Determine Premium On Redemption, Prior To Maturity																																																																																																																																	103.313%
Premium Percentage of Principal of Senior Notes, Discount Factor																																																																																																																																	0.50%
Debt Instrument, Registration Default, Incremental Additional Interest Due, Period Of Each Increase														90
Debt Instrument, Registration Default, Additional Interest Due, Maximum Annual Interest Rate														1.00%
Debt Instrument, Registration Default, Incremental Additional Interest Due, Annual Interest Rate														0.25%
Variable rate basis						3-mo. LIBOR	3-mo. LIBOR	3-mo. LIBOR	3-mo. LIBOR																						LIBOR	[1]	LIBOR	[1]												Various	Various							LIBOR	[1]	LIBOR	[1]			LIBOR	[1]	LIBOR	[1]														LIBOR	[1]	LIBOR	[1]									LIBOR	[1]	LIBOR	[1]	LIBOR	[1]	LIBOR	[1]		LIBOR	[1]	LIBOR	[1]	LIBOR	[1]	LIBOR	[1]	LIBOR		LIBOR			Various	Various					LIBOR					LIBOR
Basis spread on variable rate						1.07%	3.50%	3.50%	3.50%																						3.00%	[1]	3.00%	[1]																				1.07%	[1]	1.07%	[1]							2.25%	[1]	2.25%	[1]	2.75%	[1]	2.75%	[1]										2.50%	[1]	2.50%	[1]	2.625%	[1]	2.625%	[1]	3.50%	[1]	3.50%	[1]	3.50%	[1]	3.50%	[1]		2.01%	[1]	2.01%	[1]	2.50%	[1]	2.50%	[1]	2.25%		2.25%	2.25%	2.25%									3.50%			2.50%		2.50%	2.25%
Credit Facility, amount borrowed																																																																											548,000,000																																66,000,000			40,000,000													166,000,000	2,000,000
Long-term Debt	11,342,000,000		11,342,000,000		9,729,000,000					8,046,000,000	7,933,000,000	3,296,000,000	1,796,000,000		990,000,000	0	1,128,000,000	1,200,000,000	1,100,000,000	1,100,000,000	800,000,000	800,000,000	692,000,000	691,000,000	1,200,000,000	1,200,000,000			270,000,000	1,090,000,000	1,577,000,000		1,588,000,000		57,000,000	57,000,000	157,000,000	148,000,000	59,000,000	59,000,000				16,000,000	0			443,000,000	290,000,000	453,000,000	314,000,000	411,000,000	270,000,000	194,000,000		190,000,000		541,000,000	181,000,000	294,000,000		159,000,000										141,000,000	151,000,000		548,000,000	0	73,000,000		75,000,000										15,000,000		17,000,000		40,000,000		42,000,000			46,000,000		61,000,000		26,000,000		27,000,000		0		0	40,000,000		31,000,000	19,000,000	6,200,000,000									0
Percentage of increase at each interest rate escalation period (as a percent)																																																																																																										0.25%																0.25%
Line of Credit Facility, Maximum Borrowing Capacity																																																																																																										4,000,000													10,000,000		80,000,000	37,000,000
Letters of Credit Outstanding, Amount																																																																																																																				5,000,000		10,000,000		80,000,000						10,000,000
Percentage of applicable margin for availability fee (as a percent)																																																																																																										100.00%																100.00%
Percentage of Term Loan Entered into Interest Rate Swap																																																																																																										90.00%																85.00%
Interest rate swap fixed interest rate (as a percent)																																																																																																										2.333%																2.74%
Notional Amount of Interest Rate Derivatives	2,251,000,000		2,251,000,000		2,121,000,000																																																																																																					59,000,000																141,000,000
Proceeds from renewable energy grants			49,000,000	0																																																																																													21,000,000
Repayments of Short-term Debt																																																																																																	17,000,000
Proceeds from Construction Loans Payable																																																																										138,000,000
Proceeds from Issuance of Secured Tax Exempt Debt																																									$ 16,000,000
Interest rate, minimum																																																1.126%	1.126%	1.116%	1.116%	1.381%	1.381%					2.395%	2.395%													5.95%	5.95%		0.611%
Interest rate, maximum																																																3.991%	3.991%	4.195%	4.195%	4.256%	4.256%					3.256%	3.256%													7.31%	7.31%		2.639%

[1] L+ equals LIBOR plus x%.