Basis of Presentation (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Depreciation and amortization	$ 530	$ 500	$ 1,606	$ 1,376
Operating and maintenance	1,735	2,170	5,391	5,979
Capital expenditures			3,887	4,162
Exelon Generation Co L L C [Member]
Depreciation and amortization	218	207	643	564
Operating and maintenance	936	1,289	2,943	3,319
Capital expenditures			1,995	2,602
Commonwealth Edison Co [Member]
Depreciation and amortization	164	157	501	458
Operating and maintenance	296	313	907	882
Capital expenditures			1,074	896
PECO Energy Co [Member]
Depreciation and amortization	57	55	171	161
Operating and maintenance	162	172	480	491
Capital expenditures			374	274
Baltimore Gas and Electric Company [Member]
Depreciation and amortization	78	68	252	218
Operating and maintenance	125	172	391	460
Capital expenditures			391	419
Baltimore Gas and Electric Company [Member] | Scenario Adjustment [Member]
Depreciation and amortization			2
Operating and maintenance			4
Capital expenditures			$ 17