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Accounting for Derivative Instruments and Hedging Activities - Effect on the Company's of Accumulated OCI Balance Attributable to Cash Flow Hedge Derivatives, Net (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Derivative [Line Items]      
Beginning balance $ (1,234) $ 1,968 $ 4,446
Reclassified from accumulated OCI to income:      
Sale of NRG Yield and Renewables   25 0
Ending balance 1,658 (1,234) 1,968
Interest rate contracts | AOCI Including Portion Attributable to Noncontrolling Interest      
Derivative [Line Items]      
Beginning balance 0 (54) (66)
Reclassified from accumulated OCI to income:      
Ending balance   0 (54)
Interest rate contracts | Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent      
Reclassified from accumulated OCI to income:      
Due to realization of previously deferred amounts $ 8   12
Interest rate contracts | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent      
Reclassified from accumulated OCI to income:      
Mark-to-market of cash flow hedge accounting contracts   $ 21 $ 0