Plant Retirements (Details) (USD $)	9 Months Ended	1 Months Ended	9 Months Ended			12 Months Ended	9 Months Ended
	Sep. 30, 2012	May 31, 2012 Eddystone Generating Station [Member]	Sep. 30, 2012 Schuylkill Station Unit One [Member] MW	Sep. 30, 2012 Riverside Station Unit Six [Member] MW	Sep. 30, 2012 Exelon Generation Co L L C [Member]	May 31, 2012 Exelon Generation Co L L C [Member] Eddystone Generating Station [Member]	Sep. 30, 2012 Exelon Generation Co L L C [Member] Schuylkill Station Unit One [Member] MW	Sep. 30, 2012 Exelon Generation Co L L C [Member] Riverside Station Unit Six [Member] MW
Plant Retirements Reserve [Line Items]
Severance benefit obligation - beginning balance	$ 7,000,000				$ 7,000,000
Cash payments	(2,000,000)				(2,000,000)
Severance benefit obligation - ending balance	5,000,000				5,000,000
Plant Retirement Positions Eliminated [Abstract]
Fossil generating unit capacity to be retired			166	115			166	115
Plant Retirements Reliability Must Run Revenue [Abstract]
Monthly revenue during reliability-must-run period		$ 6,000,000				$ 6,000,000