Plant Retirements (Details) (Exelon Generation Co L L C [Member], USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2012	May 31, 2012 Eddystone Generating Station [Member]
Plant Retirements Reserve [Line Items]
Severance benefit obligation - beginning balance	$ 7,000,000
Cash payments	(2,000,000)
Severance benefit obligation - ending balance	5,000,000
Plant Retirements Reliability Must Run Revenue [Abstract]
Monthly revenue during reliability-must-run period		$ 6,000,000