Fair Value of Financial Instruments (Details 4) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011
Fair Value of Financial Instruments Disclosure [Abstract]
Decrease in fair value as a result of the credit reserve	$ 9,000,000
Decrease in fair value as a result of the credit reserve, portion recorded in OCI	(4,000,000)
Decrease in fair value as a result of the credit reserve, portion recorded in operating revenue and cost of operations	5,000,000
Credit Reserve Decrease in Fair Value			15,000,000
CreditReserve Loss in OCI			5,000,000
Credit Reserve Loss in P&L			10,000,000
Amount Of Credit Exposure To Significant Portion Of All Counterparties	620,000,000
Counterparty credit exposure, collateral held, cash and letters of credit	28,000,000
Counterparty credit exposure, net	592,000,000
Concentration of Credit Risk
Net Exposure (as a percent)	100.00%	[1]
Counterparty credit risk exposure, threshold percentage (as a percent)	10.00%
Counterparty credit risk exposure aggregate amount above threshold percentage	124,000,000
Percentage of credit risk roll-off by the end of 2012 (as a percent)	83.00%
Estimated counterparty credit risk exposure under California tolling agreements, South Central load obligations and a coal supply agreement for the next five years	$ 1,100,000,000
Derivative Asset, Fair Value Determined Using Valuation Techniques, Percentage	1.00%
Derivative Liability, Fair Value Determined Using Valuation Techniques, Percentage	1.00%
Investment grade
Concentration of Credit Risk
Net Exposure (as a percent)	63.00%	[1]
Non-investment grade
Concentration of Credit Risk
Net Exposure (as a percent)	2.00%	[1]
Non-rated
Concentration of Credit Risk
Net Exposure (as a percent)	35.00%	[1],[2]
Financial institutions
Concentration of Credit Risk
Net Exposure (as a percent)	46.00%	[1]
Utilities, energy, merchants, marketers and other
Concentration of Credit Risk
Net Exposure (as a percent)	51.00%	[1]
Coal and emissions
Concentration of Credit Risk
Net Exposure (as a percent)	1.00%	[1]
ISOs
Concentration of Credit Risk
Net Exposure (as a percent)	2.00%	[1]

[1] (a)Counterparty credit exposure excludes uranium and coal transportation contracts because of the unavailability of market prices.

[2] For non-rated counterparties, the majority are related to ISO and municipal public power entities, which are considered investment grade equivalent ratings based on NRG's internal credit ratings.