Derivative Financial Instruments (Credit Risk) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Exelon Generation Co L L C [Member]
Counter Party With Exposure [Abstract]
Cash Collateral Held	$ 206		$ 499
Letters Of Credit Held	34		45
Due From Related Parties [Abstract]
Net receivable from electric utility	38
Net receivable from affiliated electric and gas utility	38
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member]
Due From Related Parties [Abstract]
Net receivable from affiliated electric and gas utility	38
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	38
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	27
Exelon Generation Co L L C [Member] | Total Exposure Before Credit Collateral [Member]
Credit Risk [Abstract]
Investment grade	1,621
Non-investment grade	27
No external ratings - internally rated - investment grade	416
No external ratings - internally rated - non-investment grade	30
Total	2,094
Exelon Generation Co L L C [Member] | Credit Collateral [Member]
Credit Risk [Abstract]
Investment grade	172	[1]
Non-investment grade	9	[1]
No external ratings - internally rated - investment grade	1	[1]
No external ratings - internally rated - non-investment grade	2	[1]
Total	184	[1]
Exelon Generation Co L L C [Member] | Net Exposure [Member]
Credit Risk [Abstract]
Investment grade	1,449
Non-investment grade	18
No external ratings - internally rated - investment grade	415
No external ratings - internally rated - non-investment grade	28
Total	1,910
Financial institutions	256
Investor-owned utilities, marketers and power producers	684
Energy cooperative and municipalities	907
Other	63
Total	1,910
Exelon Generation Co L L C [Member] | Number Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Credit Risk [Abstract]
Investment grade	1
No external ratings - internally rated - investment grade	1
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	491
No external ratings - internally rated - investment grade	226
Total	717
Commonwealth Edison Co [Member]
Counter Party With Exposure [Abstract]
Cash Collateral Held	19
PECO Energy Co [Member]
Natural Gas Supply And Management Agreement Credit Exposure [Abstract]
Credit exposure under natural gas supply and management agreements	9
Baltimore Gas and Electric Company [Member]
Natural Gas Supply And Management Agreement Credit Exposure [Abstract]
Credit exposure under off system sales	14
Other Segments [Member]
Counter Party With Exposure [Abstract]
Cash Collateral Held	155
Letters Of Credit Held	$ 29

[1] As of December 31, 2013, credit collateral held from counterparties where Generation had credit exposure included $155 million of cash and $29 million of letters of credit