Basis of Presentation (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
Depreciation and amortization	$ 533	$ 494	$ 1,076	$ 876
Exelon Generation Co L L C [Member]
Depreciation and amortization	210	204	424	357
Commonwealth Edison Co [Member]
Depreciation and amortization	170	152	337	300
PECO Energy Co [Member]
Depreciation and amortization	56	54	113	107
Baltimore Gas and Electric Company [Member]
Depreciation and amortization	82	71	175	150
Baltimore Gas and Electric Company [Member] | Scenario Adjustment [Member]
Depreciation and amortization			$ 2