Cover - USD ($)	12 Months Ended
	Dec. 31, 2021	Feb. 24, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-15891
Entity Registrant Name	NRG Energy, Inc
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	41-1724239
Entity Address, Address Line One	910 Louisiana Street
Entity Address, City or Town	Houston
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	77002
City Area Code	713
Local Phone Number	537-3000
Title of 12(b) Security	Common Stock, par value $0.01
Trading Symbol	NRG
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 8,611,281,553
Entity Common Stock, Shares Outstanding		242,153,239
Documents Incorporated by Reference	Portions of the Registrant's definitive Proxy Statement relating to its 2022 Annual Meeting of Stockholdersare incorporated by reference into Part III of this Annual Report on Form 10-K
Entity Central Index Key	0001013871
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY