Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Operating and maintenance	$ 1,892	$ 1,841	$ 3,656	$ 3,809
Interest Expense	246	250	863	439
Exelon Generation Co L L C [Member]
Operating and maintenance	1,041	990	2,007	2,029
Interest Expense	93	85	176	138
Consolidation Percentages Detail Tagging [Abstract]
Exelon Percentage ownership of Exelon SHC, LLC	50.01%		50.01%
Commonwealth Edison Co [Member]
Electrical transmission and distribution revenue	1,080	1,280	2,238	2,669
Operating and maintenance	319	293	611	569
Interest Expense	72	71	422	150
PECO Energy Co [Member]
Operating and maintenance	155	146	319	318
Interest Expense	25	28	51	56
Baltimore Gas and Electric Company [Member]
Operating and maintenance	139	136	266	297
Interest Expense	$ 32	$ 34	$ 66	$ 75