Derivative Financial Instruments (Credit Risk) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Exelon Generation Co L L C [Member]
Counter Party With Exposure [Abstract]
Cash Collateral Held	$ 148	$ 206
Letters Of Credit Held	14	34
Credit Risk [Abstract]
Financial institutions	799
Investor-owned utilities, marketers and power producers	201
Energy cooperative and municipalities	392
Other	30
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member]
Due From Related Parties [Abstract]
Net receivable from electric utility	34
Exelon Generation Co L L C [Member] | Total Exposure Before Credit Collateral [Member]
Credit Risk [Abstract]
Investment grade	1,182
Non-investment grade	35
No external ratings - internally rated - investment grade	321
No external ratings - internally rated - non-investment grade	32
Total	1,570
Exelon Generation Co L L C [Member] | Credit Collateral [Member]
Credit Risk [Abstract]
Investment grade	117
Non-investment grade	22
No external ratings - internally rated - investment grade	0
No external ratings - internally rated - non-investment grade	9
Total	148
Exelon Generation Co L L C [Member] | Net Exposure [Member]
Credit Risk [Abstract]
Investment grade	1,065
Non-investment grade	13
No external ratings - internally rated - investment grade	321
No external ratings - internally rated - non-investment grade	23
Total	1,422
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	443
Non-investment grade	0
No external ratings - internally rated - investment grade	206
No external ratings - internally rated - non-investment grade	0
Total	649
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	1
PECO Energy Co [Member] | PECO Energy Co Affiliate [Member]
Due From Related Parties [Abstract]
Net receivable from affiliated electric and gas utility	42
Baltimore Gas and Electric Company [Member]
Natural Gas Supply And Management Agreement Credit Exposure [Abstract]
Credit exposure under off system sales	12
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	$ 41