Regulatory Matters (GenOn, GenOn Americas Generation and GenOn Mid-Atlantic) (Details) $ in Billions		9 Months Ended	12 Months Ended
	Aug. 01, 2016 USD ($)	Sep. 30, 2017 power_plant	Dec. 31, 2016 USD ($)
Regulated Operations [Abstract]
Regulatory payments sought			$ 2.5
Regulatory payments term			10 years
Public Utilities, General Disclosures [Line Items]
Out-of-market subsidy payments	$ 7.6
Out-of-market subsidy payment term	12 years
Illinois
Public Utilities, General Disclosures [Line Items]
Number of Exelon-owned nuclear power plants awarded ZECs | power_plant		2