Income Taxes - Schedule of Carryforwards and Corresponding Valuation Allowances (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Internal Revenue Service (IRS) [Member] | Commonwealth Edison Co [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards(a)	$ 0
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2034
Federal general business credits carryforwards(a)	$ 891
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(a)	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(a)	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(a)	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(a)	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(a)	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(a)	$ 0
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, Expiration Date	Dec. 31, 2034
Federal general business credits carryforwards(a)	$ 897
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	3,986
Deferred taxes on state tax attributes (net)	264
Valuation allowance on state tax attributes	$ 26
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2025
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	312
Deferred taxes on state tax attributes (net)	25
Valuation allowance on state tax attributes	$ 0
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2031
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	$ 762
Deferred taxes on state tax attributes (net)	50
Valuation allowance on state tax attributes	$ 1
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2026
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	$ 1,360
Deferred taxes on state tax attributes (net)	93
Valuation allowance on state tax attributes	$ 0
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2028
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	$ 202
Deferred taxes on state tax attributes (net)	13
Valuation allowance on state tax attributes	$ 0
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2028
State and Local Jurisdiction [Member] | Delmarva Power & Light Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	$ 654
Deferred taxes on state tax attributes (net)	44
Valuation allowance on state tax attributes	$ 0
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2030
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	$ 438
Deferred taxes on state tax attributes (net)	31
Valuation allowance on state tax attributes	$ 0
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2031
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses	$ 1,142
Deferred taxes on state tax attributes (net)	78
Valuation allowance on state tax attributes	$ 24
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2029