Debt and Capital Leases (Interest Rate Swaps) (Details 9) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)
Debt Instrument
Debt Instrument, Description of Variable Rate Basis	3 month LIBOR
Interest Rate Swap
Debt Instrument
Derivative, Notional Amount	$ 3,430
GenOn Marsh Landing
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	75.00%
Debt Instrument, Description of Variable Rate Basis	3-mo. LIBOR
GenOn Marsh Landing | Interest Rate Swap
Debt Instrument
Derivative, Fixed Interest Rate	3.244%
Derivative, Notional Amount	$ 342
Iron Springs Renewables [Member]
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	80.00%
Debt Instrument, Description of Variable Rate Basis	1-mo. LIBOR
Iron Springs Renewables [Member] | Interest Rate Swap
Debt Instrument
Derivative, Fixed Interest Rate	2.555%
Derivative, Notional Amount	$ 34
Four Brothers Holdings [Member]
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	80.00%
Debt Instrument, Description of Variable Rate Basis	1-mo. LIBOR
Four Brothers Holdings [Member] | Interest Rate Swap
Debt Instrument
Derivative, Fixed Interest Rate	2.567%
Derivative, Notional Amount	$ 141
Granite Mountain Renewables [Member]
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	80.00%
Debt Instrument, Description of Variable Rate Basis	1-mo. LIBOR
Granite Mountain Renewables [Member] | Interest Rate Swap
Debt Instrument
Derivative, Fixed Interest Rate	2.557%
Derivative, Notional Amount	$ 56
Non Recourse Debt [Member] | El Segundo Energy Center
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	75.00%
Debt Instrument, Description of Variable Rate Basis	3-mo. LIBOR
Non Recourse Debt [Member] | El Segundo Energy Center | Interest Rate Swap
Debt Instrument
Derivative, Fixed Interest Rate	2.417%
Derivative, Notional Amount	$ 330
Non Recourse Debt [Member] | NRG Solar Roadrunner LLC
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	75.00%
Debt Instrument, Description of Variable Rate Basis	3-mo. LIBOR
Non Recourse Debt [Member] | NRG Solar Roadrunner LLC | Interest Rate Swap
Debt Instrument
Derivative, Fixed Interest Rate	4.313%
Derivative, Notional Amount	$ 28
Non Recourse Debt [Member] | NRG Solar Avra Valley LLC
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	85.00%
Debt Instrument, Description of Variable Rate Basis	3-mo. LIBOR
Non Recourse Debt [Member] | NRG Solar Avra Valley LLC | Interest Rate Swap
Debt Instrument
Derivative, Fixed Interest Rate	2.333%
Derivative, Notional Amount	$ 49
Recourse Debt [Member] | NRG Energy [Member]
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	85.00%
Debt Instrument, Description of Variable Rate Basis	1-mo. LIBOR
Recourse Debt [Member] | NRG Energy [Member] | Interest Rate Swap
Debt Instrument
Derivative, Notional Amount	$ 1,000
NRG Other
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	75.00%
NRG Other | Interest Rate Swap
Debt Instrument
Derivative, Notional Amount	$ 142
Broken Bow Wind [Member] | Non Recourse Debt [Member] | EME [Member] | Interest Rate Swap
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	75.00%
Debt Instrument, Description of Variable Rate Basis	3-mo. LIBOR
Derivative, Notional Amount	$ 58
Cedro Hill Wind LLC, due in 2025 [Member] | Non Recourse Debt [Member]
Debt Instrument
Debt Instrument, Description of Variable Rate Basis	LIBOR	[1]
Cedro Hill Wind LLC, due in 2025 [Member] | Non Recourse Debt [Member] | EME [Member] | Interest Rate Swap
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	90.00%
Debt Instrument, Description of Variable Rate Basis	3-mo. LIBOR
Derivative, Notional Amount	$ 147
Crofton Bluffs [Member] | Non Recourse Debt [Member] | EME [Member] | Interest Rate Swap
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	75.00%
Debt Instrument, Description of Variable Rate Basis	3-mo. LIBOR
Derivative, Notional Amount	$ 38
Laredo Ridge Wind, LLC, due in 2026 [Member] | Non Recourse Debt [Member] | EME [Member] | Interest Rate Swap
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	75.00%
Derivative, Fixed Interest Rate	2.31%
Debt Instrument, Description of Variable Rate Basis	3-mo. LIBOR
Derivative, Notional Amount	$ 79
Tapestry Wind LLC due in 2021 [Member] | Non Recourse Debt [Member]
Debt Instrument
Debt Instrument, Description of Variable Rate Basis	LIBOR	[1]
Tapestry Wind LLC due in 2021 [Member] | Non Recourse Debt [Member] | EME [Member] | Interest Rate Swap
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	75.00%
Derivative, Fixed Interest Rate	2.21%
Debt Instrument, Description of Variable Rate Basis	3-mo. LIBOR
Derivative, Notional Amount	$ 155
Tapestry Wind LLC due in 2029 [Member] | Non Recourse Debt [Member] | EME [Member] | Interest Rate Swap
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	50.00%
Derivative, Fixed Interest Rate	3.57%
Debt Instrument, Description of Variable Rate Basis	3-mo. LIBOR
Derivative, Notional Amount	$ 60
Viento Funding II, Inc., due in 2023 [Member]
Debt Instrument
Debt Instrument, Description of Variable Rate Basis	6 - month LIBOR
Viento Funding II, Inc., due in 2023 [Member] | Non Recourse Debt [Member]
Debt Instrument
Debt Instrument, Description of Variable Rate Basis	LIBOR	[1]
Viento Funding II, Inc., due in 2023 [Member] | Non Recourse Debt [Member] | EME [Member] | Interest Rate Swap
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	90.00%
Debt Instrument, Description of Variable Rate Basis	6-mo. LIBOR
Derivative, Notional Amount	$ 160
Viento Funding II, Inc., due in 2028 [Member] | Non Recourse Debt [Member] | EME [Member] | Interest Rate Swap
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	90.00%
Derivative, Fixed Interest Rate	4.985%
Debt Instrument, Description of Variable Rate Basis	6-mo. LIBOR
Derivative, Notional Amount	$ 65
Walnut Creek Energy, LLC, due in 2023 [Member]
Debt Instrument
Debt Instrument, Description of Variable Rate Basis	1 - month LIBOR
Walnut Creek Energy, LLC, due in 2023 [Member] | Non Recourse Debt [Member]
Debt Instrument
Debt Instrument, Description of Variable Rate Basis	LIBOR	[1]
Walnut Creek Energy, LLC, due in 2023 [Member] | Non Recourse Debt [Member] | EME [Member] | Interest Rate Swap
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	75.00%
Debt Instrument, Description of Variable Rate Basis	3-mo. LIBOR
Derivative, Notional Amount	$ 276
WCEP Holdings, LLC, due in 2023 [Member] | Non Recourse Debt [Member] | EME [Member] | Interest Rate Swap
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	90.00%
Derivative, Fixed Interest Rate	4.003%
Debt Instrument, Description of Variable Rate Basis	3-mo. LIBOR
Derivative, Notional Amount	$ 46
Alta Wind Asset Management [Member] | Non Recourse Debt [Member] | Alta Wind Holdings [Member] | Interest Rate Swap
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	100.00%
Derivative, Fixed Interest Rate	2.47%
Debt Instrument, Description of Variable Rate Basis	3-mo. LIBOR
Derivative, Notional Amount	$ 18
Maturity - June 14, 2028 | Non Recourse Debt [Member] | South Trent Wind LLC
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	75.00%
Debt Instrument, Description of Variable Rate Basis	3-mo. LIBOR
Maturity - June 14, 2028 | Non Recourse Debt [Member] | South Trent Wind LLC | Interest Rate Swap
Debt Instrument
Derivative, Fixed Interest Rate	4.95%
Derivative, Notional Amount	$ 21
Maturity - June 14, 2020 | Non Recourse Debt [Member] | South Trent Wind LLC
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	75.00%
Debt Instrument, Description of Variable Rate Basis	3-mo. LIBOR
Maturity - June 14, 2020 | Non Recourse Debt [Member] | South Trent Wind LLC | Interest Rate Swap
Debt Instrument
Derivative, Fixed Interest Rate	3.265%
Derivative, Notional Amount	$ 43
Maturity July 15, 2036 [Member] | DGPV 4 [Member]
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	85.00%
Debt Instrument, Description of Variable Rate Basis	3-mo. LIBOR
Maturity July 15, 2036 [Member] | DGPV 4 [Member] | Interest Rate Swap
Debt Instrument
Derivative, Notional Amount	$ 19
Maturity - December 31, 2029 [Member] | Non Recourse Debt [Member] | NRG Solar Alpine LLC
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	85.00%
Debt Instrument, Description of Variable Rate Basis	3-mo. LIBOR
Maturity - December 31, 2029 [Member] | Non Recourse Debt [Member] | NRG Solar Alpine LLC | Interest Rate Swap
Debt Instrument
Derivative, Fixed Interest Rate	2.744%
Derivative, Notional Amount	$ 115
Maturity - June 30, 2025 [Member] | Non Recourse Debt [Member] | NRG Solar Alpine LLC
Debt Instrument
Percentage of Debt Hedged by Interest Rate Derivatives	85.00%
Debt Instrument, Description of Variable Rate Basis	3-mo. LIBOR
Maturity - June 30, 2025 [Member] | Non Recourse Debt [Member] | NRG Solar Alpine LLC | Interest Rate Swap
Debt Instrument
Derivative, Fixed Interest Rate	2.421%
Derivative, Notional Amount	$ 8

[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%.