Severance - Ongoing Severance Plans (Details) - Exelon Generation Co L L C [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Corporate Restructuring Severance Benefit Obligation [Line Items]
Severance Costs	$ 2	$ 20
Corporate, Non-Segment [Member]
Corporate Restructuring Severance Benefit Obligation [Line Items]
Severance Costs	$ 1