Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Operating and maintenance	$ 1,764	$ 1,968
Interest Expense	617	189
Exelon Generation Co L L C [Member]
Operating and maintenance	965	1,039
Interest Expense	82	54
Consolidation Percentages Detail Tagging [Abstract]
Exelon Percentage ownership of Exelon SHC, LLC	50.01%
Commonwealth Edison Co [Member]
Electrical transmission and distribution revenue	1,159	1,387
Operating and maintenance	292	276
Interest Expense	350	79
PECO Energy Co [Member]
Operating and maintenance	164	173
Interest Expense	26	28
Baltimore Gas and Electric Company [Member]
Operating and maintenance	124	154
Interest Expense	$ 33	$ 41