Income Taxes - Reconciliation to Effective Tax Rate (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	5.40%	3.40%	4.40%	3.80%
Qualified nuclear decommissioning trust fund income	5.10%	0.20%	6.50%	(0.10%)
Amortization of investment tax credit, including deferred taxes on basis difference	(0.70%)	(0.90%)	(0.60%)	(1.10%)
Plant basis differences	(1.70%)	(3.00%)	(1.50%)	(2.80%)
Production tax credits and other credits	(0.90%)	(1.70%)	(0.80%)	(2.30%)
Noncontrolling interests	0.10%	(1.50%)	(0.30%)	(1.10%)
Excess deferred tax amortization	(7.80%)	(5.20%)	(5.80%)	(5.60%)
Tax Cuts and Jobs Act of 2017		(1.30%)		(0.60%)
Other	1.90%	(0.20%)	0.70%	(1.70%)
Effective income tax rate	22.40%	10.80%	23.60%	9.50%
Exelon Generation Co L L C [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	5.50%	4.30%	3.60%	3.40%
Qualified nuclear decommissioning trust fund income	16.20%	0.50%	14.70%	(0.40%)
Amortization of investment tax credit, including deferred taxes on basis difference	(1.90%)	(2.40%)	(1.10%)	(3.30%)
Plant basis differences	0.00%	0.00%	0.00%	0.00%
Production tax credits and other credits	(2.80%)	(4.90%)	(1.80%)	(7.20%)
Noncontrolling interests	0.40%	(4.50%)	(0.80%)	(3.50%)
Excess deferred tax amortization	0.00%	0.00%	0.00%	0.00%
Tax Cuts and Jobs Act of 2017		(1.70%)		(0.90%)
Other	0.20%	(1.30%)	(0.40%)	(1.30%)
Effective income tax rate	38.60%	11.00%	35.20%	7.80%
Commonwealth Edison Co [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	8.20%	8.10%	8.20%	8.10%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.20%)	(0.20%)	(0.20%)	(0.20%)
Plant basis differences	(0.60%)	(0.10%)	(0.60%)	0.00%
Production tax credits and other credits	0.00%	(0.10%)	0.00%	(0.10%)
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(9.00%)	(7.60%)	(8.80%)	(7.50%)
Tax Cuts and Jobs Act of 2017		(0.70%)		(0.30%)
Other	0.40%	0.40%	0.20%	0.10%
Effective income tax rate	19.80%	20.80%	19.80%	21.10%
PECO Energy Co [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	(1.20%)	(3.40%)	0.20%	(3.60%)
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	0.00%	(0.10%)	0.00%	(0.10%)
Plant basis differences	(5.90%)	(17.20%)	(6.40%)	(15.60%)
Production tax credits and other credits	0.00%	0.00%	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(2.70%)	(0.30%)	(2.60%)	(2.70%)
Tax Cuts and Jobs Act of 2017		0.00%		0.00%
Other	0.10%	(1.10%)	(0.10%)	(0.40%)
Effective income tax rate	11.30%	(1.10%)	12.10%	(1.40%)
Baltimore Gas and Electric Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	6.50%	6.50%	6.40%	6.40%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	(0.20%)	(0.10%)	(0.10%)
Plant basis differences	(1.50%)	(0.70%)	(1.00%)	(0.70%)
Production tax credits and other credits	(0.10%)	0.00%	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(7.90%)	(7.20%)	(7.90%)	(8.20%)
Tax Cuts and Jobs Act of 2017		0.10%		0.00%
Other	1.70%	0.80%	0.20%	0.20%
Effective income tax rate	19.60%	20.30%	18.60%	18.60%
Pepco Holdings LLC [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	4.80%	6.20%	4.70%	5.50%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.20%)	(0.20%)	(0.20%)	(0.20%)
Plant basis differences	(1.70%)	(1.20%)	(1.70%)	(1.80%)
Production tax credits and other credits	0.00%	0.00%	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(19.40%)	(11.30%)	(19.40%)	(11.00%)
Tax Cuts and Jobs Act of 2017		0.80%		0.50%
Other	0.90%	(0.10%)	0.30%	(0.10%)
Effective income tax rate	5.40%	15.20%	4.70%	13.90%
Potomac Electric Power Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	2.00%	4.70%	2.00%	3.70%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	(0.10%)	(0.10%)	(0.10%)
Plant basis differences	(2.10%)	(2.00%)	(2.00%)	(2.50%)
Production tax credits and other credits	0.00%	0.00%	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(18.30%)	(11.70%)	(18.10%)	(12.10%)
Tax Cuts and Jobs Act of 2017		0.00%		0.00%
Other	0.50%	(0.40%)	0.50%	(0.40%)
Effective income tax rate	3.00%	11.50%	3.30%	9.60%
Delmarva Power and Light Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	7.00%	6.50%	6.70%	6.40%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.20%)	(0.30%)	(0.20%)	(0.30%)
Plant basis differences	(0.30%)	0.00%	(0.60%)	(0.70%)
Production tax credits and other credits	0.00%	0.00%	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(15.70%)	(11.20%)	(15.60%)	(9.40%)
Tax Cuts and Jobs Act of 2017		0.00%		0.00%
Other	0.00%	0.10%	0.40%	0.40%
Effective income tax rate	11.80%	16.10%	11.70%	17.40%
Atlantic City Electric Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	7.00%	7.60%	6.90%	7.20%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.30%)	(0.30%)	(0.30%)	(0.30%)
Plant basis differences	(2.20%)	(0.20%)	(2.20%)	(1.30%)
Production tax credits and other credits	0.00%	0.00%	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(23.10%)	(8.80%)	(23.40%)	(8.80%)
Tax Cuts and Jobs Act of 2017		0.00%		0.00%
Other	(2.40%)	0.70%	2.00%	(1.10%)
Effective income tax rate	0.00%	20.00%	4.00%	16.70%