Long-Term Debt (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended									1 Months Ended		9 Months Ended	1 Months Ended				9 Months Ended					1 Months Ended				6 Months Ended	9 Months Ended								9 Months Ended				9 Months Ended			9 Months Ended			1 Months Ended			3 Months Ended			1 Months Ended					1 Months Ended	9 Months Ended								6 Months Ended									9 Months Ended				9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended					9 Months Ended					9 Months Ended							9 Months Ended			1 Months Ended						9 Months Ended		6 Months Ended	9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended				3 Months Ended	6 Months Ended	9 Months Ended		3 Months Ended	6 Months Ended	9 Months Ended	1 Months Ended		9 Months Ended				1 Months Ended			1 Months Ended
	Sep. 30, 2011		Sep. 30, 2010	Sep. 30, 2011		Sep. 30, 2010	Dec. 31, 2010		Sep. 30, 2011 West Holdings PPA [Member]	Sep. 30, 2011 West Holdings PPA [Member]	Sep. 30, 2011 West Holding Collateral Agent [Member]	Sep. 30, 2011 West Holdings Working Capital Facility [Member]	Nov. 18, 2011 West Holdings Working Capital Facility [Member]	Sep. 30, 2011 West Holdings Working Capital Facility [Member]	Sep. 30, 2011 7.625% Senior notes, due 2019 and 7.875% Senior notes, due 2021 day	May 31, 2011 7.875% Senior notes, due 2021	May 24, 2011 7.875% Senior notes, due 2021	Sep. 30, 2011 7.875% Senior notes, due 2021 Recourse Debt [Member]	Dec. 31, 2010 7.875% Senior notes, due 2021 Recourse Debt [Member]	Sep. 30, 2011 7.875% Senior notes, due 2021 Prior to May 15, 2016	Sep. 30, 2011 7.875% Senior notes, due 2021 May 15, 2016 to May 14, 2017	Sep. 30, 2011 7.875% Senior notes, due 2021 May 15, 2017 to May 14, 2018	Sep. 30, 2011 7.875% Senior notes, due 2021 May 15, 2018 to May 14, 2019	Sep. 30, 2011 7.875% Senior notes, due 2021 May 15, 2019 and thereafter	May 31, 2011 7.625% Senior notes, due 2019	May 24, 2011 7.625% Senior notes, due 2019	Sep. 30, 2011 7.625% Senior notes, due 2019 Recourse Debt [Member]	Dec. 31, 2010 7.625% Senior notes, due 2019 Recourse Debt [Member]	Jun. 30, 2011 7.625% Senior notes, due 2019 Prior To May 15, 2014	Sep. 30, 2011 7.625% Senior notes, due 2019 Prior To May 15, 2014	Sep. 30, 2011 7.625% Senior notes, due 2019 May 15, 2014 to May 14, 2015	Sep. 30, 2011 7.625% Senior notes, due 2019 May 15, 2015 to May 14, 2016	Sep. 30, 2011 7.625% Senior notes, due 2019 May 15, 2016 and thereafter	Sep. 30, 2011 8.25% Senior notes, due 2020 Recourse Debt [Member]	Dec. 31, 2010 8.25% Senior notes, due 2020 Recourse Debt [Member]	Sep. 30, 2011 8.50% Senior notes, due 2019 Recourse Debt [Member]	Dec. 31, 2010 8.50% Senior notes, due 2019 Recourse Debt [Member]	Sep. 30, 2011 7.625% Senior notes, due 2018	Jan. 26, 2011 7.625% Senior notes, due 2018	Sep. 30, 2011 7.625% Senior notes, due 2018 Recourse Debt [Member]	Dec. 31, 2010 7.625% Senior notes, due 2018 Recourse Debt [Member]	Sep. 30, 2011 7.625% Senior notes, due 2018 Prior to January 15, 2018	Sep. 30, 2011 7.375% Senior notes, due 2017 Recourse Debt [Member]	Dec. 31, 2010 7.375% Senior notes, due 2017 Recourse Debt [Member]	Sep. 30, 2011 7.375% Senior notes, due 2016	Sep. 30, 2011 7.375% Senior notes, due 2016 Recourse Debt [Member]	Dec. 31, 2010 7.375% Senior notes, due 2016 Recourse Debt [Member]	May 31, 2011 7.375% Senior notes, due 2016 Part One	May 31, 2011 7.375% Senior notes, due 2016 Part Two	Jun. 30, 2011 7.375% Senior notes, due 2016 Part Three	Jun. 30, 2011 7.250% Senior notes, due 2014	Sep. 30, 2011 7.250% Senior notes, due 2014 Recourse Debt [Member]	Dec. 31, 2010 7.250% Senior notes, due 2014 Recourse Debt [Member]	Jan. 31, 2011 7.250% Senior notes, due 2014 Part One	Jan. 31, 2011 7.250% Senior notes, due 2014 Part Two	Feb. 28, 2011 7.250% Senior notes, due 2014 Part Three	Sep. 30, 2011 Senior Credit Facility Due 2018 [Member] Recourse Debt [Member]	Dec. 31, 2010 Senior Credit Facility Due 2018 [Member] Recourse Debt [Member]	Mar. 31, 2011 Term loan facility, due 2013 - 2015	Sep. 30, 2011 Term loan facility, due 2013 - 2015 Recourse Debt [Member]		Dec. 31, 2010 Term loan facility, due 2013 - 2015 Recourse Debt [Member]		Sep. 30, 2011 Term loan facility, due 2013 - 2015 Recourse Debt [Member] Minimum [Member]		Sep. 30, 2011 Term loan facility, due 2013 - 2015 Recourse Debt [Member] Maximum [Member]		Jun. 30, 2011 Term loan facility, due 2013 - 2015 Letter of Credit [Member]	Sep. 30, 2011 Term loan facility, due 2013 - 2015 Letter of Credit [Member] Minimum [Member]		Sep. 30, 2011 Term loan facility, due 2013 - 2015 Letter of Credit [Member] Maximum [Member]		Sep. 30, 2011 Indian River Power LLC, tax-exempt bonds, due 2040 Recourse Debt [Member]	Dec. 31, 2010 Indian River Power LLC, tax-exempt bonds, due 2040 Recourse Debt [Member]	Sep. 30, 2011 Indian River Power LLC, tax-exempt bonds, due 2045 Recourse Debt [Member]	Dec. 31, 2010 Indian River Power LLC, tax-exempt bonds, due 2045 Recourse Debt [Member]	Sep. 30, 2011 Sussex County, Delaware tax-exempt bond financing	Sep. 30, 2011 Delaware Economic Development Authority tax-exempt bond financing	Sep. 30, 2011 Dunkirk Power LLC, tax-exempt bonds, due 2042 Recourse Debt [Member]	Dec. 31, 2010 Dunkirk Power LLC, tax-exempt bonds, due 2042 Recourse Debt [Member]	Sep. 30, 2011 NRG Peaker Finance Co. LLC, bonds, due 2019 Non Recourse Debt [Member]	Dec. 31, 2010 NRG Peaker Finance Co. LLC, bonds, due 2019 Non Recourse Debt [Member]	Sep. 30, 2011 NRG Energy Center Minneapolis LLC, senior secured notes, due 2013, 2017, and 2025 Non Recourse Debt [Member]	Dec. 31, 2010 NRG Energy Center Minneapolis LLC, senior secured notes, due 2013, 2017, and 2025 Non Recourse Debt [Member]	Sep. 30, 2011 Ivanpah Credit Agreement	Apr. 05, 2011 Ivanpah Credit Agreement	Sep. 30, 2011 Solar Partners I, due 2014 and 2033 Non Recourse Debt [Member]	Dec. 31, 2010 Solar Partners I, due 2014 and 2033 Non Recourse Debt [Member]	Sep. 30, 2011 Solar Partners I, due June 27, 2014		Sep. 30, 2011 Solar Partners I, due June 27, 2033	Sep. 30, 2011 Solar Partners II, due 2014 and 2038 Non Recourse Debt [Member]	Dec. 31, 2010 Solar Partners II, due 2014 and 2038 Non Recourse Debt [Member]	Sep. 30, 2011 Solar Partners II, due February 27, 2014		Sep. 30, 2011 Solar Partners II, due February 27, 2038	Sep. 30, 2011 Solar Partners VIII, due 2014 and 2038 Non Recourse Debt [Member]	Dec. 31, 2010 Solar Partners VIII, due 2014 and 2038 Non Recourse Debt [Member]	Sep. 30, 2011 Solar Partners VIII, due October 27, 2014		Sep. 30, 2011 Solar Partners VIII, due October 27, 2038	Sep. 30, 2011 Agua Caliente Financing Agreement [Member]	Aug. 05, 2011 Agua Caliente Financing Agreement [Member]	Sep. 30, 2011 Agua Caliente Financing Agreement [Member] Non Recourse Debt [Member]	Dec. 31, 2010 Agua Caliente Financing Agreement [Member] Non Recourse Debt [Member]	Aug. 23, 2011 West Holdings Credit Agreement [Member]	Aug. 31, 2011 West Holdings Credit Agreement Tranche A [Member]	Sep. 30, 2011 West Holdings Credit Agreement Tranche A [Member]	Aug. 23, 2011 West Holdings Credit Agreement Tranche A [Member]	Aug. 23, 2011 West Holdings Credit Agreement Tranche B [Member]	Sep. 30, 2011 West Holdings Credit Agreement Tranche B [Member] Minimum [Member]	Sep. 30, 2011 West Holdings Credit Agreement Tranche B [Member] Maximum [Member]	Sep. 30, 2011 Equity bridge loan facility, due 2011 Non Recourse Debt [Member]	Dec. 31, 2010 Equity bridge loan facility, due 2011 Non Recourse Debt [Member]	Jun. 30, 2011 Equity bridge loan facility, due 2011 NRG Connecticut Peaking LLC	Sep. 30, 2011 NINA TANE facility Non Recourse Debt [Member]	Dec. 31, 2010 NINA TANE facility Non Recourse Debt [Member]	Sep. 30, 2011 NINA Shaw facility Non Recourse Debt [Member]	Dec. 31, 2010 NINA Shaw facility Non Recourse Debt [Member]	Sep. 30, 2011 South Trent Wind LLC, financing agreement, due 2020 Non Recourse Debt [Member]	Dec. 31, 2010 South Trent Wind LLC, financing agreement, due 2020 Non Recourse Debt [Member]	Sep. 30, 2011 NRG Solar Blythe LLC, credit agreement, due 2028 Non Recourse Debt [Member]	Dec. 31, 2010 NRG Solar Blythe LLC, credit agreement, due 2028 Non Recourse Debt [Member]	Sep. 30, 2011 Other Non Recourse Debt [Member]	Dec. 31, 2010 Other Non Recourse Debt [Member]	Sep. 30, 2011 Financing [Member] 2011 Senior Credit Facility	Jun. 30, 2011 Financing [Member] 2011 Senior Credit Facility	Sep. 30, 2011 Financing [Member] 2011 Senior Credit Facility	Sep. 30, 2011 Financing [Member] 2011 Senior Credit Facility Minimum [Member]	Sep. 30, 2010 2011 Senior Credit Facility Line of Credit [Member]	Jun. 30, 2011 2011 Senior Credit Facility Line of Credit [Member]	Sep. 30, 2011 2011 Senior Credit Facility Line of Credit [Member]	May 31, 2011 Roadrunner Financing Agreement year	May 25, 2011 Roadrunner Financing Agreement	Sep. 30, 2011 Roadrunner Financing Agreement Non Recourse Debt [Member]	Dec. 31, 2010 Roadrunner Financing Agreement Non Recourse Debt [Member]	Sep. 30, 2011 Roadrunner Financing Agreement Bridge Loan [Member]	May 25, 2011 Roadrunner Financing Agreement Bridge Loan [Member]	May 31, 2011 Roadrunner Financing Agreement Letter of Credit [Member]	Sep. 30, 2011 Roadrunner Financing Agreement Letter of Credit [Member]	May 25, 2011 Roadrunner Financing Agreement Letter of Credit [Member]	Apr. 30, 2011 Roadrunner Financing Agreement Interest Rate Swap [Member]	May 25, 2011 Roadrunner Financing Agreement Minimum [Member]	May 25, 2011 Roadrunner Financing Agreement Maximum [Member]	Sep. 30, 2011 CVSR Financing Agreement [Member]	Sep. 30, 2011 Recourse Debt [Member]	Dec. 31, 2010 Recourse Debt [Member]	Sep. 30, 2011 Non Recourse Debt [Member]	Dec. 31, 2010 Non Recourse Debt [Member]
Long-term debt disclosure
CreditReserve Loss in OCI				$ 3
Long-term debt	9,185			9,185			9,104											1,200	0								800	0						1,100	1,100	691	690			1,200	0		1,090	1,100		0	2,400					0	1,205				1,592	0		0	[1]	1,759	[1]										57	1	126	66			59	59	210	206	153	163			210	0				221	0				195	0						108	0			106		60			0	61		0	144	0	23	76	78	28	29	23	20										46	0										7,915	8,380	1,270	724
Sale Energie GmbH, Schkopau capital lease, due 2021	104			104			107
Subtotal	9,289			9,289			9,211
Less current maturities	81			81			463
Total long-term debt and capital leases	9,208			9,208			8,748
Funded letter of credit	0	[1]		0	[1]		1,300	[1]
Debt instrument, principal amount																	1,200									800													1,200																																																																																							1,600		1,600						21				47
Interest rate																		7.875%									7.625%							8.25%		8.50%				7.625%			7.375%			7.375%						7.25%																					6.00%		5.375%				5.875%																													2.4165%
Interest rate, minimum																																																																																			5.95%				1.126%					1.116%					1.381%							2.915%
Interest rate, maximum																																																																																			7.31%				3.991%					4.195%					4.256%							3.256%
Variable rate basis																																																												LIBOR								LIBOR													LIBOR				U.S. Treasury																												LIBOR			LIBOR		LIBOR		LIBOR		LIBOR						LIBOR				LIBOR	LIBOR		LIBOR							LIBOR
Basis spread on variable rate																																																									3.00%							1.75%	[2]	3.25%	[2]		1.75%	[2]	3.25%	[2]									1.07%				0.375%																		0.375%								0.125%	0.25%	2.00%			2.00%		6.00%		2.50%		2.50%				3.00%		3.00%	1.00%			2.75%			2.01%								2.01%	2.76%	0.375%
Percentage of principal amount that is the base redemption price prior to maturity (as a percent)																				100.00%										100.00%												100.00%
Percentage of principal amount paid as a premium on redemption of notes prior to maturity (as a percent)																				1.00%										1.00%												1.00%
Percentage of principal amount used to determine premium on redemption prior to maturity (as a percent)																				103.938%										103.813%
Percentage above Treasury rate over the principal amount of the note used as a discount (as a percent)																				0.50%									0.50%													0.50%
Redemption of senior notes																																																1,700.0	0.4	666.0				945.0	2.0	253.0
Redemption percentage (as a percent)																																																103.938%	102.938%	103.688%				102.063%	100.063%	101.813%
Loss on extinguishment of the Senior Notes	32		1	175		2																																							115						28																																																																															(13)
Net proceeds from issuance of debt															2,000																																																														56	60
Maximum redeemable percentage of principal prior to maturity (as a percent)																				35.00%										35.00%
Redemption percentage, prior to maturity (as a percent)																				107.875%	103.938%	102.625%	101.313%	100.00%					107.625%		103.813%	101.906%	100.00%
Period following registration default, additional interest will be paid (in days)															90
Incremental increase in interest rate on outstanding principal following registration default (as a percent)															0.25%
Maximum additional interest rate on outstanding principal following registration default (as a percent)															1.00%
Repayments of debt																																																																																																																			61
Repayment to first lien lenders under Term Loan Facility																																																											149
Subsequent event date																																																																																																																															Jul. 01, 2011
Credit facility maturity date																																																																																																																																			July 1, 2016
Debt instrument maturity date																May 15, 2021									May 15, 2019													Jan. 15, 2018																																																																																										Jul. 01, 2018					Nov. 30, 2031
Percentage of face value debt was issued at (as a percent)																																																																																																																																99.75%
Percentage of loan to be repaid on quarterly basis (as a percent)																																																																																																																																0.25%
Extinguishment of Debt, Amount																																																																																																																														19
Frequency of periodic payment																																																																																																																																quarterly
Credit Facility, amount borrowed																																																																																					626				153	[3]	57			129	[3]	92			111	[3]	84	108							480
Weighted average interest rate on amounts borrowed (as a percent)																																																																																									1.678%		3.641%			1.609%		3.925%			1.996%		4.021%
Percentage of increase at each interest rate escalation period (as a percent)																																																																																																											0.125%																										0.25%
Frequency of interest rate escalation (in years)																																																																																																																																					5
Maximum period which interest rate escalation is applicable (in years)																																																																																																																																					15
Line of Credit Facility, Maximum Borrowing Capacity										90	48			10																																																																							1,627	1,600			159	[3]	392			132	[3]	387			117	[3]	440	967	967			540																										2,300									5				1,200
Letters of Credit Outstanding, Amount									30			7																																																																																																																								1,949								2
Percentage of applicable margin for availability fee (as a percent)																																																																																																																																											100.00%
Amount outstanding under construction and term loan																																																																																																																																									46
Interest rate swap entered into as percentage of outstanding loan amount (as a percent)													75.00%																																																																																																																																	75.00%
Interest rate swap fixed interest rate (as a percent)																																																																																																																																														4.313%
Notional amount of interest rate derivatives	$ 1,265			$ 1,265			$ 2,782							$ 135																																																																																																																																$ 36

[1] On July 1, 2011, the Term loan facility, due 2013-2015 and Funded letter of credit were repaid and replaced, as described below under Senior Credit Facility.

[2] On July 1, 2011, the Term loan facility and Funded letter of credit were repaid and replaced, as described below under Senior Credit Facility.

[3] The cash portion of the loan is fully drawn; additional amounts will be utilized for capitalized interest.