Income Taxes - Schedule of Carryforwards and Corresponding Valuation Allowances (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Amount	$ 184	[1]
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Amount	184	[1]
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Commonwealth Edison Co [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Amount	0	[1]
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | PECO Energy Co [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Amount	0	[1]
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Amount	0	[1]
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforward	3,141	[2]
State net operating losses and other credit carryforwards	169
Valuation allowance on state tax attributes	50
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforward	1,693	[3]
State net operating losses and other credit carryforwards	96
Valuation allowance on state tax attributes	48
State and Local Jurisdiction [Member] | Commonwealth Edison Co [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforward	0
State net operating losses and other credit carryforwards	0
Valuation allowance on state tax attributes	0
State and Local Jurisdiction [Member] | PECO Energy Co [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforward	170
State net operating losses and other credit carryforwards	11
Valuation allowance on state tax attributes	0
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforward	730
State net operating losses and other credit carryforwards	39
Valuation allowance on state tax attributes	$ 1

[1] Exelon’s state net operating losses and other carryforwards, which are presented on a post-apportioned basis, will expire beginning in 2015

[2] Generation’s state net operating losses and other carryforwards, which are presented on a post-apportioned basis, will expire beginning in 2015.

[3] PECO’s state net operating losses will expire beginning in 2031.