Benefit Plans and Other Postretirement Benefits (Details 2) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits
Amounts recognized in balance sheet
Current liabilities	$ 0	$ 0
Non-current liabilities	288	280
Amounts recognized in accumulated OCI
Net loss/(gain)	94	68
Prior service cost/(credit)	3	3
Other changes in plan assets and benefit obligations recognized in other comprehensive income
Net actuarial loss/(gain)	28	(31)
Amortization of net actuarial (gain)/loss	(2)	(2)	$ 6
Prior service credit	0	(1)
Other Comprehensive (Income) Loss, Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit), before Tax	0	0
Defined Benefit Plan, Curtailment Recognized in OCI	0	0
Total recognized in other comprehensive loss	(26)	34
Total recognized in net periodic pension cost/(credit) and other comprehensive loss/(income)	41	(8)
Estimated unrecognized loss for NRG's pension plan that will be amortized from accumulated OCI to net periodic cost over the next fiscal year	4
Significant components of NRG's domestic pension plan
Projected benefit obligation	1,241	1,196	1,305
Accumulated benefit obligation	1,174	1,115
Fair value of plan assets	953	916	988
Other Postretirement Benefits
Amounts recognized in balance sheet
Current liabilities	8	12
Non-current liabilities	120	166
Amounts recognized in accumulated OCI
Net loss/(gain)	(11)	(9)
Prior service cost/(credit)	(45)	(9)
Other changes in plan assets and benefit obligations recognized in other comprehensive income
Net actuarial loss/(gain)	(2)	(31)
Amortization of net actuarial (gain)/loss	0	(1)	0
Prior service credit	(41)	(7)
Other Comprehensive (Income) Loss, Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit), before Tax	5	5
Defined Benefit Plan, Curtailment Recognized in OCI	0	(11)
Total recognized in other comprehensive loss	38	45
Total recognized in net periodic pension cost/(credit) and other comprehensive loss/(income)	36	(37)
Defined Benefit Plan, Future Amortization of Gain (Loss)	1
Defined Benefit Plan, Future Amortization of Prior Service Cost (Credit)	8
Significant components of NRG's domestic pension plan
Projected benefit obligation	128	178	238
Fair value of plan assets	$ 0	$ 0	$ 0