Income Taxes - Remeasurement of Deferred Income Tax Balances - Federal (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Income Tax Expense (Benefit)	$ 774	$ 118	$ (126)
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Income Tax Expense (Benefit)	516	(108)	(1,376)
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Income Tax Expense (Benefit)	163	168	417
PECO Energy Co [Member]
Income Taxes [Line Items]
Income Tax Expense (Benefit)	65	6	104
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Income Tax Expense (Benefit)	79	74	218
Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Income Tax Expense (Benefit)	38	33	217
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Income Tax Expense (Benefit)	16	11	105
Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
Income Tax Expense (Benefit)	22	22	71
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Income Tax Expense (Benefit)	$ 0	12	$ 26
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member]
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes		8,624
Increase (Decrease) in Regulatory Liabilities		7,315
Income Tax Expense (Benefit)		1,309
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes		1,895
Income Tax Expense (Benefit)		1,895
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes		2,819
Increase (Decrease) in Regulatory Liabilities		2,818
Income Tax Expense (Benefit)		1
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | PECO Energy Co [Member]
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes		1,407
Increase (Decrease) in Regulatory Liabilities		1,394
Income Tax Expense (Benefit)		13
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes		1,120
Increase (Decrease) in Regulatory Liabilities		1,124
Income Tax Expense (Benefit)		(4)
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes		1,944
Increase (Decrease) in Regulatory Liabilities		1,979
Income Tax Expense (Benefit)		(35)
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes		968
Increase (Decrease) in Regulatory Liabilities		976
Income Tax Expense (Benefit)		(8)
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes		540
Increase (Decrease) in Regulatory Liabilities		545
Income Tax Expense (Benefit)		(5)
RemeasurementOfDeferredIncomeTaxesDueToTaxReform [Member] | Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Increase (Decrease) in Deferred Income Taxes		456
Increase (Decrease) in Regulatory Liabilities		458
Income Tax Expense (Benefit)		$ (2)