Income Taxes (Provision - Details 1) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current
State	$ 17	$ 6	$ 8
Total — current	17	6	8
Deferred
U.S. Federal	3	1,020	(50)
State	(6)	315	41
Foreign	2	1	4
Total — deferred	(1)	1,336	(5)
Income tax expense/(benefit)	$ 16	$ 1,342	$ 3
Effective income tax rate (as a percent)	(1.80%)	(26.30%)	2.20%
Domestic and foreign components of income from continuing operations before income tax expense
U.S.	$ (886)	$ (5,105)	$ 126
Foreign	11	11	9
Income/(loss) before income taxes	$ 875	$ 5,094	$ (135)
U.S. federal statutory rate (as a percent)	35.00%	35.00%	35.00%
Reconciliation of the U.S. federal statutory rate to NRG's effective rate from continuing operations
Income/(loss) before income taxes	$ 875	$ 5,094	$ (135)
Tax at 35%	(306)	(1,783)	47
State taxes	11	(218)	9
Foreign operations	10	1	1
Federal and state tax credits, excluding PTCs	0	(5)	(1)
Valuation allowance	306	3,039	6
Impact of non-taxable equity earnings	22	(10)	(11)
Book goodwill impairment	0	(340)	0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	1	(3)	(2)
Production tax credit	(26)	(33)	(48)
Recognition of uncertain tax benefits	2	(15)	(30)
Effective Income Tax Rate Reconciliation, Tax Expense Attributable to Partnerships	(1)	12	4
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	1	19	22
Other	(4)	(2)	6
Income tax expense/(benefit)	$ 16	$ 1,342	$ 3
Effective income tax rate (as a percent)	(1.80%)	(26.30%)	2.20%