Income Taxes - Income Tax Provision (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Current
State	$ 48	$ 22	$ 2
Foreign	3	4	4
Total — current	51	26	6
Deferred
U.S. Federal	569	168	(3,000)
State	36	60	(340)
Foreign	16	(3)	0
Total — deferred	621	225	(3,340)
Total income tax expense/(benefit)	672	251	(3,334)
Domestic and foreign components of income from continuing operations before income tax expense
U.S.	2,759	749	771
Foreign	100	12	15
Income from Continuing Operations Before Income Taxes	2,859	761	786
Reconciliation of the U.S. federal statutory rate to NRG's effective rate from continuing operations
Income from continuing operations before income taxes	2,859	761	786
Tax at federal statutory tax rate	600	160	165
Foreign operations	(3)	0	0
State taxes	111	18	13
Permanent differences	8	8	(9)
Changes in valuation allowance	(29)	24	(3,492)
Deferred impact of state tax rate changes	(10)	2	12
Recognition of uncertain tax benefits	(10)	3	(10)
Return to provision adjustments	5	36	0
Other	0	0	(13)
Total income tax expense/(benefit)	$ 672	$ 251	$ (3,334)
Effective income tax rate (as a percent)	23.50%	33.00%	(424.20%)