Chapter 11 Cases (GenOn and GenOn Americas Generation) - Reorganization Items (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reorganization [Line Items]
Legal and other professional advisory fees	$ (29)		$ (55)
Write-off of debt premiums and credit reserves	0		103
Reorganization items, net	(29)	$ 0	48	$ 0
GenOn Americas Generation
Reorganization [Line Items]
Legal and other professional advisory fees	0		(1)
Write-off of debt premiums and credit reserves	0		43
Reorganization items, net	$ 0	$ 0	$ 42	$ 0