Income Taxes - Narrative (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
	Jun. 05, 2019	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits, Period Increase (Decrease)			$ (33)
Effective income tax rate		15.60%		14.50%	20.70%	11.60%
Exelon Generation Co L L C [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		17.40%		20.10%	28.60%	13.80%
Commonwealth Edison Co [Member]
Income Tax Additional Narrative Information [Line Items]
Unrecognized Tax Benefits, Period Increase (Decrease)			$ (2)
Effective income tax rate		18.40%		21.20%	19.30%	21.10%
PECO Energy Co [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		9.10%		(1.60%)	11.10%	(1.50%)
Baltimore Gas and Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		17.90%		22.20%	18.40%	19.60%
Pepco Holdings LLC [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		6.90%		2.10%	5.70%	7.70%
Potomac Electric Power Company [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		4.90%		(2.30%)	4.00%	3.90%
Delmarva Power and Light Company [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		13.20%		13.20%	12.10%	15.90%
Atlantic City Electric Company [Member]
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate		3.10%		11.60%	2.20%	13.60%
ILLINOIS
Income Tax Additional Narrative Information [Line Items]
Effective income tax rate	10.49%				9.50%