Income Taxes - Narrative (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
	Jun. 05, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		27.60%	22.40%	(8.50%)	23.60%
Decrease in Unrecognized Tax Benefits is Reasonably Possible		$ 411		$ 411
Tax Adjustments, Settlements, and Unusual Provisions				76
Income Tax Expense (Benefit)		$ 219	$ 144	$ (75)	$ 454
Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		38.30%	38.60%	(18.80%)	35.20%
Decrease in Unrecognized Tax Benefits is Reasonably Possible		$ 411		$ 411
Tax Adjustments, Settlements, and Unusual Provisions				73
Income Tax Expense (Benefit)		$ 329	$ 78	$ (59)	$ 301
Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		(306.70%)	19.80%	43.40%	19.80%
Income Tax Expense (Benefit)		$ 46	$ 46	$ 82	$ 85
PECO Energy Co [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		(21.90%)	11.30%	4.80%	12.10%
Income Tax Expense (Benefit)		$ (7)	$ 13	$ 9	$ 37
Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		(129.40%)	19.60%	7.60%	18.60%
Income Tax Expense (Benefit)		$ (22)	$ 11	$ 18	$ 47
Pepco Holdings LLC [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		(1242.90%)	5.40%	(60.30%)	4.70%
Income Tax Expense (Benefit)		$ (87)	$ 6	$ (76)	$ 11
Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		(72.70%)	3.00%	(21.10%)	3.30%
Income Tax Expense (Benefit)		$ (24)	$ 2	$ (19)	$ 4
Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		311.10%	11.80%	(45.50%)	11.70%
Income Tax Expense (Benefit)		$ (28)	$ 4	$ (20)	$ 11
Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		220.00%	0.00%	3200.00%	4.00%
Income Tax Expense (Benefit)		$ (33)	$ 0	$ (32)	$ 1
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%