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Changes in Capital Structure - NRG Common Stock Dividends (Details) - $ / shares
3 Months Ended 12 Months Ended
Apr. 15, 2020
Mar. 31, 2020
Mar. 31, 2019
Dec. 31, 2019
Subsequent Event [Line Items]        
Common stock dividends proposed annual amount (in usd per share)   $ 1.20   $ 0.12
Dividends per common share (in usd per share)   $ 0.30 $ 0.03  
Subsequent Event        
Subsequent Event [Line Items]        
Common stock dividends declared (in usd per share) $ 0.30      
Minimum        
Subsequent Event [Line Items]        
Common stock, annual dividend growth rate, percentage   700.00%    
Maximum        
Subsequent Event [Line Items]        
Common stock, annual dividend growth rate, percentage   9.00%