Derivative Financial Instruments (Credit Risk) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013
Exelon Generation Co L L C [Member]
Credit Risk [Abstract]
Financial institutions	$ 386
Investor-owned utilities, marketers and power producers	761
Energy cooperative and municipalities	926
Other	53
Total	2,126
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member]
Due From Related Parties [Abstract]
Net receivable from electric utility	41
Exelon Generation Co L L C [Member] | PECO Energy Co Affiliate [Member]
Due From Related Parties [Abstract]
Net receivable from affiliated electric and gas utility	44
Exelon Generation Co L L C [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Due From Related Parties [Abstract]
Net receivable from affiliated electric and gas utility	33
Exelon Generation Co L L C [Member] | Total Exposure Before Credit Collateral [Member]
Credit Risk [Abstract]
Investment grade	1,744
Non-investment grade	40
No external ratings - internally rated - investment grade	456
No external ratings - internally rated - non-investment grade	62
Total	2,302
Exelon Generation Co L L C [Member] | Credit Collateral [Member]
Credit Risk [Abstract]
Investment grade	139
Non-investment grade	31
No external ratings - internally rated - investment grade	5
No external ratings - internally rated - non-investment grade	1
Total	176
Exelon Generation Co L L C [Member] | Net Exposure [Member]
Credit Risk [Abstract]
Investment grade	1,605
Non-investment grade	9
No external ratings - internally rated - investment grade	451
No external ratings - internally rated - non-investment grade	61
Total	2,126
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	462
Non-investment grade	0
No external ratings - internally rated - investment grade	247
No external ratings - internally rated - non-investment grade	0
Total	709
PECO Energy Co [Member]
Natural Gas Supply And Management Agreement Credit Exposure [Abstract]
Credit exposure under natural gas supply and management agreements	0
Baltimore Gas and Electric Company [Member]
Natural Gas Supply And Management Agreement Credit Exposure [Abstract]
Credit exposure under off system sales	$ 2