Preferred Securities (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Temporary Equity [Line Items]
Shares outstanding	874,720	874,720
Dollar amount	$ 87,000,000	$ 87,000,000
Series A Preferred Stock [Member]
Temporary Equity [Line Items]
Shares outstanding	300,000	300,000
Dollar amount	30,000,000	30,000,000
Redemption price	$ 106.00
Dividend yield	$ 3.80
Series B Preferred Stock [Member]
Temporary Equity [Line Items]
Shares outstanding	150,000	150,000
Dollar amount	15,000,000	15,000,000
Redemption price	$ 102.00
Dividend yield	$ 4.30
Series C Preferred Stock [Member]
Temporary Equity [Line Items]
Shares outstanding	274,720	274,720
Dollar amount	27,000,000	27,000,000
Redemption price	$ 112.50
Dividend yield	$ 4.40
Series D Preferred Stock [Member]
Temporary Equity [Line Items]
Shares outstanding	150,000	150,000
Dollar amount	$ 15,000,000	$ 15,000,000
Redemption price	$ 104.00
Dividend yield	$ 4.68
Preferred Stock [Member]
Preferred Securities Additional Narrative Information [Line Items]
Shares authorized	100,000,000	100,000,000
Commonwealth Edison Co [Member] | Preferred Stock [Member]
Preferred Securities Additional Narrative Information [Line Items]
Shares authorized	850,000	850,000
Commonwealth Edison Co [Member] | Cumulative Preferred Stock [Member]
Preferred Securities Additional Narrative Information [Line Items]
Shares authorized	6,810,451	6,810,451
PECO Energy Co [Member] | Cumulative Preferred Stock [Member]
Preferred Securities Additional Narrative Information [Line Items]
Shares authorized	15,000,000	15,000,000