Quarterly Data (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Earnings Per Share Basic [Abstract]
Average common shares outstanding - basic	856	853	856	779
Earnings Per Share, Basic	$ 0.57	$ 0.34	$ 0.57	$ 0.62
Earnings Per Share Diluted
Average common shares outstanding - diluted	860	856	859	781
Earnings Per Share, Diluted	$ 0.57	$ 0.33	$ 0.57	$ 0.62
Selected Quarterly Financial Information [Line Items]
Revenues	$ 6,141	$ 5,966	$ 12,223	$ 10,656
Operating Income (Loss)	1,005	714	1,513	1,073
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	497	289	498	490
Exelon Generation Co L L C [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	4,070	3,765	7,603	6,508
Operating Income (Loss)	603	384	539	656
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	328	165	310	332
Commonwealth Edison Co [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	1,080	1,281	2,239	2,670
Operating Income (Loss)	232	142	440	368
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	96	42	14	129
PECO Energy Co [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	672	715	1,567	1,590
Operating Income (Loss)	138	151	341	327
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	78	80	200	177
Baltimore Gas and Electric Company [Member]
Selected Quarterly Financial Information [Line Items]
Revenues	653	616	1,533	1,312
Operating Income (Loss)	69	52	233	41
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 25	$ 16	$ 106	$ (14)