Consolidated Statement of Changes in Shareholders Equity (Unaudited) (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Accumulated Other Comprehensive (Loss) Income, Net
Other comprehensive income, income taxes	$ (41,000,000)	$ (221,000,000)	$ 119,000,000
Exelon Generation Co L L C [Member]
Adoption of the fair value option for financial assets and liabilities, income taxes			286,000,000
Transfer of AmerGen pension and non-pension postretirement benefit plans to Exelon, income taxes		17,000,000
Other comprehensive income, income taxes	(102,000,000)	199,000,000	908,000,000
PECO Energy Co [Member]
Other comprehensive income, income taxes	0	(1,000,000)	(1,000,000)
Commonwealth Edison Co [Member]
Other comprehensive income, income taxes	$ 0	$ 0	$ 3,000,000