Basis of Presentation (GenOn, GenOn Americas Generation and GenOn Mid-Atlantic) (Details) - MW	1 Months Ended
	Jun. 30, 2017	Sep. 30, 2017	Dec. 31, 2016
Basis of Presentation
Generation capacity (in MW)		15,395
Senior Notes
Basis of Presentation
Percentage aggregate principal amount of borrowings outstanding threshold (greater than) (as percent)	93.00%
Pittsburg
Basis of Presentation
Generation capacity (in MW)			1,029
GenOn Americas Generation, LLC
Basis of Presentation
Generation capacity (in MW)		6,878
GenOn Americas Generation, LLC | Senior Notes
Basis of Presentation
Percentage aggregate principal amount of borrowings outstanding threshold (greater than) (as percent)	93.00%
GenOn Mid-Atlantic, LLC
Basis of Presentation
Generation capacity (in MW)		4,605