Income Taxes - Schedule of Carryforwards and Corresponding Valuation Allowances (Details) $ in Millions	Dec. 31, 2018 USD ($)
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	$ 811	[1]
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	816
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Commonwealth Edison Co [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	0
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | PECO Energy Co [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	0
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	0
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Pepco Holdings LLC [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	0
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Potomac Electric Power Company [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	0
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Delmarva Power & Light Company [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	0
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member] | Atlantic City Electric Company [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards	0
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	4,103	[2]
Deferred taxes on state tax attributes (net)	272
Valuation allowance on state tax attributes	35
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	1,544	[2]
Deferred taxes on state tax attributes (net)	104
Valuation allowance on state tax attributes	26
State and Local Jurisdiction [Member] | Commonwealth Edison Co [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	0
Deferred taxes on state tax attributes (net)	0
Valuation allowance on state tax attributes	0
State and Local Jurisdiction [Member] | PECO Energy Co [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	224	[3]
Deferred taxes on state tax attributes (net)	18
Valuation allowance on state tax attributes	0
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	395	[4]
Deferred taxes on state tax attributes (net)	26
Valuation allowance on state tax attributes	1
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	1,492	[5]
Deferred taxes on state tax attributes (net)	102
Valuation allowance on state tax attributes	6
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	192	[6]
Deferred taxes on state tax attributes (net)	12
Valuation allowance on state tax attributes	0
State and Local Jurisdiction [Member] | Delmarva Power & Light Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	772	[7]
Deferred taxes on state tax attributes (net)	52
Valuation allowance on state tax attributes	0
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	365	[8]
Deferred taxes on state tax attributes (net)	26
Valuation allowance on state tax attributes	$ 0

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[4] .

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[8] .