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Capital Structure - Changes in NRG's Common Stock Issued and Outstanding (Details) - shares
 1 Months Ended 3 Months Ended 12 Months Ended
Mar. 09, 2023
Jan. 31, 2024
Dec. 31, 2023
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Schedule of Stock by Class, Equity [Roll Forward]            
Preferred shares, balance beginning (in shares)   650,000   0    
Preferred shares, outstanding, beginning balance (in shares)   650,000   0    
Preferred shares, balance as of end of period (in shares)     650,000 650,000 0  
Preferred shares, outstanding , ending balance (in shares)     650,000 650,000 0  
Beginning balance, common shares issued (in shares)   267,330,470   423,897,001    
Beginning balance, treasury shares (in shares)   (59,199,520)   (194,335,971)    
Beginning balance, common shares outstanding (in shares)   208,130,950   229,561,030 243,753,899 244,231,933
Share repurchases (in shares)       (22,730,940) (14,685,521) (1,084,752)
Retirement of treasury stock (in shares)     157,676,142 0    
Ending balance, common shares issued (in shares)     267,330,470 267,330,470 423,897,001  
Ending balance, treasury shares (in shares)     (59,199,520) (59,199,520) (194,335,971)  
Ending balance, common shares outstanding (in shares)     208,130,950 208,130,950 229,561,030 243,753,899
Subsequent Event            
Schedule of Stock by Class, Equity [Roll Forward]            
Share repurchases (in shares)   (770,205)        
Ending balance, common shares outstanding (in shares)   208,021,012        
Long-term Incentive Plan            
Schedule of Stock by Class, Equity [Roll Forward]            
Shares issued under LTIPs (in shares)       1,109,611 349,827 489,326
Long-term Incentive Plan | Subsequent Event            
Schedule of Stock by Class, Equity [Roll Forward]            
Shares issued under LTIPs (in shares)   660,267        
Employee Stock Purchase Plan            
Schedule of Stock by Class, Equity [Roll Forward]            
Shares issued under ESPP (in shares)       191,249 142,825 117,392
Preferred Stock            
Schedule of Stock by Class, Equity [Roll Forward]            
Preferred shares, balance beginning (in shares)   650,000        
Preferred shares, outstanding, beginning balance (in shares)   650,000        
Preferred shares, balance as of end of period (in shares)     650,000 650,000    
Preferred shares, outstanding , ending balance (in shares)     650,000 650,000    
Preferred Stock | Subsequent Event            
Schedule of Stock by Class, Equity [Roll Forward]            
Preferred shares, balance as of end of period (in shares)   650,000        
Preferred shares, outstanding , ending balance (in shares)   650,000        
Preferred Stock | Series A Preferred Stock            
Schedule of Stock by Class, Equity [Roll Forward]            
Issuance of Series A Preferred Stock (in shares) 650,000     650,000    
Common Stock            
Schedule of Stock by Class, Equity [Roll Forward]            
Beginning balance, common shares issued (in shares)   267,330,470   423,897,001 423,547,174 423,057,848
Beginning balance, common shares outstanding (in shares)   208,130,950        
Retirement of treasury stock (in shares)         (157,676,142)  
Ending balance, common shares issued (in shares)     267,330,470 267,330,470 423,897,001 423,547,174
Ending balance, common shares outstanding (in shares)     208,130,950 208,130,950    
Common Stock | Subsequent Event            
Schedule of Stock by Class, Equity [Roll Forward]            
Shares issued under LTIPs (in shares)   660,267        
Retirement of treasury stock (in shares)   (770,205)        
Ending balance, common shares issued (in shares)   267,220,532        
Common Stock | Long-term Incentive Plan            
Schedule of Stock by Class, Equity [Roll Forward]            
Shares issued under LTIPs (in shares)       1,109,611 349,827 489,326
Treasury Stock            
Schedule of Stock by Class, Equity [Roll Forward]            
Beginning balance, treasury shares (in shares)   (59,199,520)   (194,335,971) (179,793,275) (178,825,915)
Shares issued under ESPP (in shares)       191,249 142,825 117,392
Share repurchases (in shares)       (22,730,940) (14,685,521) (1,084,752)
Retirement of treasury stock (in shares)       157,676,142    
Ending balance, treasury shares (in shares)     (59,199,520) (59,199,520) (194,335,971) (179,793,275)
Treasury Stock | Subsequent Event            
Schedule of Stock by Class, Equity [Roll Forward]            
Shares issued under LTIPs (in shares)   0        
Share repurchases (in shares)   (770,205)        
Retirement of treasury stock (in shares)   770,205        
Ending balance, treasury shares (in shares)   (59,199,520)        
Treasury Stock | Long-term Incentive Plan            
Schedule of Stock by Class, Equity [Roll Forward]            
Shares issued under LTIPs (in shares)       0 0 0