Income Taxes - Narrative (Details) - USD ($) $ in Millions		3 Months Ended
	Jun. 05, 2019	Mar. 31, 2020	Mar. 31, 2019
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		(345.90%)	24.20%
Decrease in Unrecognized Tax Benefits is Reasonably Possible		$ 411
Tax Adjustments, Settlements, and Unusual Provisions		76
Income Tax Expense (Benefit)		$ (294)	$ 310
Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		71.10%	34.30%
Decrease in Unrecognized Tax Benefits is Reasonably Possible		$ 411
Tax Adjustments, Settlements, and Unusual Provisions		73
Income Tax Expense (Benefit)		$ (389)	$ 224
Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		17.60%	20.30%
Income Tax Expense (Benefit)		$ 36	$ 40
PECO Energy Co [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		9.70%	13.00%
Income Tax Expense (Benefit)		$ 15	$ 25
Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		18.50%	18.40%
Income Tax Expense (Benefit)		$ 41	$ 36
Pepco Holdings LLC [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		9.20%	4.10%
Income Tax Expense (Benefit)		$ 11	$ 5
Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		8.80%	3.50%
Income Tax Expense (Benefit)		$ 5	$ 2
Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		13.50%	11.70%
Income Tax Expense (Benefit)		$ 7	$ 7
Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		7.10%	0.00%
Income Tax Expense (Benefit)		$ 1	$ 0
Internal Revenue Service (IRS) [Member]
Income Tax Additional Narrative Information [Line Items]
Income Tax Expense (Benefit)		(67)
Internal Revenue Service (IRS) [Member] | Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Income Tax Expense (Benefit)		$ (67)
ILLINOIS
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate	10.49%	9.50%