Income Taxes - Schedule of Carryforwards and Corresponding Valuation Allowances (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Operating Loss Carryforwards [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible	$ 411
Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible	411
Internal Revenue Service (IRS) [Member] | General Business Tax Credit Carryforward [Member]
Operating Loss Carryforwards [Line Items]
Federal general business credits carryforwards and other carryforwards	858
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 and other carryforwards	852
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 and other 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 and other 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 and other 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 and other 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 and other 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 and other carryforwards	0
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses and other carryforwards	5,202
Deferred taxes on state tax attributes (net)	324
Valuation allowance on state tax attributes	$ 27
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2034
Tax Credit Carryforward, Expiration Date	Dec. 31, 2034
State and Local Jurisdiction [Member] | ILLINOIS
Operating Loss Carryforwards [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2029
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses and other carryforwards	$ 1,118
Deferred taxes on state tax attributes (net)	76
Valuation allowance on state tax attributes	$ 23
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2034
Tax Credit Carryforward, Expiration Date	Dec. 31, 2034
State and Local Jurisdiction [Member] | PECO Energy Co [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses and other carryforwards	$ 616
Deferred taxes on state tax attributes (net)	49
Valuation allowance on state tax attributes	$ 1
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2032
Tax Credit Carryforward, Expiration Date	Dec. 31, 2021
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses and other carryforwards	$ 902
Deferred taxes on state tax attributes (net)	59
Valuation allowance on state tax attributes	$ 0
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2033
Tax Credit Carryforward, Expiration Date	Dec. 31, 2021
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses and other carryforwards	$ 1,436
Deferred taxes on state tax attributes (net)	98
Valuation allowance on state tax attributes	$ 0
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2029
Decrease in Unrecognized Tax Benefits is Reasonably Possible	$ 14
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses and other carryforwards	63
Deferred taxes on state tax attributes (net)	4
Valuation allowance on state tax attributes	$ 0
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2029
State and Local Jurisdiction [Member] | Delmarva Power & Light Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses and other carryforwards	$ 728
Deferred taxes on state tax attributes (net)	49
Valuation allowance on state tax attributes	$ 0
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2032
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member]
Operating Loss Carryforwards [Line Items]
State net operating losses and other carryforwards	$ 531
Deferred taxes on state tax attributes (net)	38
Valuation allowance on state tax attributes	$ 0
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2031