Income Taxes - Reconciliation to Effective Tax Rate (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 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	6.40%	(1.20%)	5.10%	1.70%
Qualified nuclear decommissioning trust fund income	3.20%	2.40%	5.30%	0.90%
Amortization of investment tax credit, including deferred taxes on basis difference	(4.10%)	(0.60%)	(1.90%)	(0.90%)
Plant basis differences	(1.70%)	(2.50%)	(1.60%)	(2.70%)
Production tax credits and other credits	(1.20%)	(1.20%)	(1.00%)	(1.80%)
Noncontrolling interests	(2.20%)	(1.10%)	(1.00%)	(1.10%)
Excess deferred tax amortization	(6.50%)	(6.80%)	(6.00%)	(6.10%)
Tax Cuts and Jobs Act of 2017		1.30%		0.20%
Other	0.70%	3.20%	0.80%	0.40%
Effective income tax rate	15.60%	14.50%	20.70%	11.60%
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	5.20%	(9.00%)	4.20%	(2.60%)
Qualified nuclear decommissioning trust fund income	7.10%	5.80%	11.90%	2.60%
Amortization of investment tax credit, including deferred taxes on basis difference	(8.90%)	(1.10%)	(4.00%)	(2.20%)
Plant basis differences	0.00%	0.00%	0.00%	0.00%
Production tax credits and other credits	(2.70%)	(2.90%)	(2.10%)	(5.10%)
Noncontrolling interests	(4.80%)	(2.80%)	(2.30%)	(3.20%)
Excess deferred tax amortization	0.00%	0.00%	0.00%	0.00%
Tax Cuts and Jobs Act of 2017		3.50%		1.30%
Other	0.50%	5.60%	(0.10%)	2.00%
Effective income tax rate	17.40%	20.10%	28.60%	13.80%
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	8.10%	8.30%	8.20%	8.20%
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	(0.20%)	(0.20%)	(0.20%)	(0.20%)
Plant basis differences	(1.00%)	(0.30%)	(0.70%)	(0.10%)
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	(9.90%)	(7.80%)	(9.20%)	(7.60%)
Tax Cuts and Jobs Act of 2017		0.00%		(0.20%)
Other	0.40%	0.30%	0.20%	0.10%
Effective income tax rate	18.40%	21.20%	19.30%	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	(0.30%)	(3.60%)	0.00%	(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	(7.50%)	(15.20%)	(6.80%)	(15.40%)
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	(3.60%)	(4.60%)	(2.90%)	(3.40%)
Tax Cuts and Jobs Act of 2017		0.00%		0.00%
Other	(0.50%)	0.90%	(0.20%)	0.00%
Effective income tax rate	9.10%	(1.60%)	11.10%	(1.50%)
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	6.30%	7.30%	6.40%	6.60%
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	(0.10%)	0.00%	(0.10%)	(0.10%)
Plant basis differences	(1.10%)	(0.80%)	(1.10%)	(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	(8.00%)	(7.90%)	(7.90%)	(8.10%)
Tax Cuts and Jobs Act of 2017		0.00%		0.00%
Other	(0.20%)	2.60%	0.10%	0.90%
Effective income tax rate	17.90%	22.20%	18.40%	19.60%
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%	0.20%	4.80%	2.70%
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	(0.20%)	(0.20%)	(0.20%)	(0.20%)
Plant basis differences	(1.80%)	(2.00%)	(1.80%)	(1.90%)
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	(17.70%)	(17.70%)	(18.60%)	(14.50%)
Tax Cuts and Jobs Act of 2017		0.20%		0.30%
Other	0.80%	0.60%	0.50%	0.30%
Effective income tax rate	6.90%	2.10%	5.70%	7.70%
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	1.90%	1.00%	2.00%	2.40%
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%)	(0.10%)	(0.10%)	(0.10%)
Plant basis differences	(2.60%)	(3.40%)	(2.30%)	(2.90%)
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	(16.30%)	(21.20%)	(17.30%)	(16.50%)
Tax Cuts and Jobs Act of 2017		0.10%		0.00%
Other	1.00%	0.30%	0.70%	0.00%
Effective income tax rate	4.90%	(2.30%)	4.00%	3.90%
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	6.60%	6.60%	6.70%	6.50%
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%)	(0.30%)	(0.20%)	(0.30%)
Plant basis differences	(0.60%)	(0.70%)	(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	(13.50%)	(14.00%)	(15.00%)	(11.00%)
Tax Cuts and Jobs Act of 2017		0.00%		0.00%
Other	(0.10%)	0.60%	0.20%	0.40%
Effective income tax rate	13.20%	13.20%	12.10%	15.90%
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	6.90%	7.30%	6.90%	7.30%
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	(1.90%)	(1.30%)	(2.00%)	(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	(23.30%)	(15.40%)	(23.40%)	(14.00%)
Tax Cuts and Jobs Act of 2017		0.00%		0.00%
Other	0.70%	0.30%	0.00%	0.90%
Effective income tax rate	3.10%	11.60%	2.20%	13.60%