Commitments and Contingencies (GenOn, GenOn Americas Generation and GenOn Mid-Atlantic) (Details) shares in Thousands	1 Months Ended
	Jun. 30, 2013 case	Sep. 30, 2017 shares	Dec. 13, 2016	May 31, 2016 case	Jul. 31, 2011 case
GenOn Energy | Senior Notes | GenOn Senior Notes, due 2017
Chapter Eleven Proceedings
Interest rate (as percent)		7.875%	7.875%
GenOn Energy | Senior Notes | GenOn Senior Notes, due 2018
Chapter Eleven Proceedings
Interest rate (as percent)		9.50%	9.50%
GenOn Energy | Senior Notes | GenOn Senior Notes, due 2020
Chapter Eleven Proceedings
Interest rate (as percent)		9.875%	9.875%
GenOn Americas Generation | Senior Notes | GenOn Americas Generation Senior Notes, due 2021
Chapter Eleven Proceedings
Interest rate (as percent)		8.50%	8.50%
GenOn Americas Generation | Senior Notes | GenOn Americas Generation Senior Notes, due 2031
Chapter Eleven Proceedings
Interest rate (as percent)		9.125%	9.125%
Natural Gas Litigation
Loss Contingencies [Line Items]
Number of cases	5				5
Natural Gas Litigation | Nevada
Loss Contingencies [Line Items]
Number of cases					4
Number of cases ended due to petition for writ of certiorari being denied	1
Natural Gas Litigation | Kansas
Loss Contingencies [Line Items]
Number of cases				1
Bankruptcy | Chapter Eleven Proceedings
Chapter Eleven Proceedings
GenOn Energy Holdings common stock shares reserved for unresolved claims (in shares) | shares		461
Number of reserved shares for disputed Chapter 11 claims converted into reserved of GenOn common stock (in shares) | shares		1,300
Number of reserved shares for disputed Chapter 11 claims converted into reserved of NRG common stock (in shares) | shares		159