Derivative Financial Instruments (Credit Risk) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Exelon Generation Co L L C [Member]
Credit Risk [Abstract]
Financial institutions	$ 355
Investor-owned utilities, marketers and power producers	743
Energy cooperative and municipalities	916
Other	52
Total	2,066
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member]
Due From Related Parties [Abstract]
Net receivable from electric utility	33
Exelon Generation Co L L C [Member] | Total Exposure Before Credit Collateral [Member]
Credit Risk [Abstract]
Investment grade	1,767
Non-investment grade	16
No external ratings - internally rated - investment grade	472
No external ratings - internally rated - non-investment grade	18
Total	2,273
Exelon Generation Co L L C [Member] | Credit Collateral [Member]
Credit Risk [Abstract]
Investment grade	191
Non-investment grade	9
No external ratings - internally rated - investment grade	6
No external ratings - internally rated - non-investment grade	1
Total	207
Exelon Generation Co L L C [Member] | Net Exposure [Member]
Credit Risk [Abstract]
Investment grade	1,576
Non-investment grade	7
No external ratings - internally rated - investment grade	466
No external ratings - internally rated - non-investment grade	17
Total	2,066
Exelon Generation Co L L C [Member] | Number Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Credit Risk [Abstract]
Investment grade	1
Non-investment grade	0
No external ratings - internally rated - investment grade	1
No external ratings - internally rated - non-investment grade	0
Total	2
Exelon Generation Co L L C [Member] | Net Exposure Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Credit Risk [Abstract]
Investment grade	478
Non-investment grade	0
No external ratings - internally rated - investment grade	238
No external ratings - internally rated - non-investment grade	0
Total	716
PECO Energy Co [Member]
Natural Gas Supply And Management Agreement Credit Exposure [Abstract]
Credit exposure under natural gas supply and management agreements	9
PECO Energy Co [Member] | PECO Energy Co Affiliate [Member]
Due From Related Parties [Abstract]
Net receivable from affiliated electric and gas utility	30
Baltimore Gas and Electric Company [Member]
Natural Gas Supply And Management Agreement Credit Exposure [Abstract]
Credit exposure under off system sales	1
Baltimore Gas and Electric Company [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Due From Related Parties [Abstract]
Net receivable from affiliated electric and gas utility	$ 39