Commitments and Contigencies (Contingencies) (Details 4) - USD ($)		3 Months Ended	9 Months Ended	12 Months Ended
		Sep. 30, 2010	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2016
Loss Contingencies
Environmental Projects			$ 1,000,000
MD Department of Environment v. Chalk Point [Member]
Loss Contingencies
Civil Penalties			1,000,000
Midwest Generation New Source Review [Member]
Loss Contingencies
Civil Penalties		$ 37,500
Telephone Consumer Protection Act Purported Class Actions [Member]
Loss Contingencies
Loss Contingency, Damages Sought, Value			$ 1,500
CDWR and SDGE v Sunrise Power [Member]
Loss Contingencies
Loss Contingency, Damages Sought, Value				$ 1,200,000
Remaining Term				70 months
GenOn Senior Notes Due in 2017 [Member] | Non Recourse Debt [Member]
Loss Contingencies
Debt Instrument, Interest Rate, Stated Percentage	[1]				7.875%
GenOn senior notes, due 2018 | Non Recourse Debt [Member]
Loss Contingencies
Debt Instrument, Interest Rate, Stated Percentage	[1]				9.50%
GenOn senior notes, due 2020 | Non Recourse Debt [Member]
Loss Contingencies
Debt Instrument, Interest Rate, Stated Percentage	[1]				9.875%
GenOn Americas Generation Senior Notes Due in 2021 [Member] | Non Recourse Debt [Member]
Loss Contingencies
Debt Instrument, Interest Rate, Stated Percentage	[1]				8.50%
GenOn Americas Generation senior notes, due 2031 | Non Recourse Debt [Member]
Loss Contingencies
Debt Instrument, Interest Rate, Stated Percentage	[1]				9.125%

[1] As of December 31, 2016, L+ equals 3 month LIBOR plus x%, with the exception of the Viento term loan, which is 6 month LIBOR plus x% and the Alpine term loan, the NRG Marsh Landing term loan, the Walnut Creek loan, and 2023 Term Loan Facility, which are 1 month LIBOR plus x%.