Derivative Financial Instruments (Credit Risk) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Exelon Generation Co L L C [Member]
Counter Party With Exposure [Abstract]
Cash Collateral Held		$ 206
Letters Of Credit Held		34
Credit Risk [Abstract]
Financial institutions	185
Investor-owned utilities, marketers and power producers	360
Energy cooperative and municipalities	729
Other	22
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member]
Due From Related Parties [Abstract]
Net receivable from electric utility	6
Exelon Generation Co L L C [Member] | Total Exposure Before Credit Collateral [Member]
Credit Risk [Abstract]
Investment grade	1,095
Non-investment grade	12
No external ratings - internally rated - investment grade	286
No external ratings - internally rated - non-investment grade	21
Total	1,414
Exelon Generation Co L L C [Member] | Credit Collateral [Member]
Credit Risk [Abstract]
Investment grade	103
Non-investment grade	9
No external ratings - internally rated - investment grade	2
No external ratings - internally rated - non-investment grade	4
Total	118
Exelon Generation Co L L C [Member] | Net Exposure [Member]
Credit Risk [Abstract]
Investment grade	992
Non-investment grade	3
No external ratings - internally rated - investment grade	284
No external ratings - internally rated - non-investment grade	17
Total	1,296
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	417
Non-investment grade	0
No external ratings - internally rated - investment grade	189
No external ratings - internally rated - non-investment grade	0
Total	606
Commonwealth Edison Co [Member]
Counter Party With Exposure [Abstract]
Cash Collateral Held	19
Commonwealth Edison Co [Member] | Net Exposure [Member]
Credit Risk [Abstract]
Total	2
PECO Energy Co [Member]
Natural Gas Supply And Management Agreement Credit Exposure [Abstract]
Credit exposure under natural gas supply and management agreements	6
PECO Energy Co [Member] | PECO Energy Co Affiliate [Member]
Due From Related Parties [Abstract]
Net receivable from affiliated electric and gas utility	23
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	36
Baltimore Gas and Electric Company [Member] | Net Exposure [Member]
Credit Risk [Abstract]
Total	$ 38