Income Taxes - Reconciliation to Effective Tax Rate (Details)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	34.00%	3.90%
Qualified nuclear decommissioning trust fund income	(235.80%)	7.20%
Amortization of investment tax credit, including deferred taxes on basis difference	(4.50%)	(0.50%)
Plant basis differences	(23.00%)	(1.40%)
Production tax credits and other credits	(9.90%)	(0.80%)
Noncontrolling interests	10.60%	(0.60%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	(79.10%)
Excess deferred tax amortization	(71.70%)	(4.70%)
Other	12.50%	0.10%
Effective income tax rate	(345.90%)	24.20%
Exelon Generation Co L L C [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	0.70%	3.10%
Qualified nuclear decommissioning trust fund income	36.40%	14.20%
Amortization of investment tax credit, including deferred taxes on basis difference	0.50%	(0.90%)
Plant basis differences	0.00%	0.00%
Production tax credits and other credits	1.30%	(1.50%)
Noncontrolling interests	(1.60%)	(1.10%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	12.20%
Excess deferred tax amortization	0.00%	0.00%
Other	0.60%	(0.50%)
Effective income tax rate	71.10%	34.30%
Commonwealth Edison Co [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	8.30%	8.20%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.20%)	(0.20%)
Plant basis differences	(1.10%)	(0.50%)
Production tax credits and other credits	(0.20%)	0.00%
Noncontrolling interests	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%
Excess deferred tax amortization	(10.50%)	(8.50%)
Other	0.30%	0.30%
Effective income tax rate	17.60%	20.30%
PECO Energy Co [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	0.10%	1.00%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	0.00%	0.00%
Plant basis differences	(8.40%)	(6.70%)
Production tax credits and other credits	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%
Excess deferred tax amortization	(3.00%)	(2.50%)
Other	0.00%	0.20%
Effective income tax rate	9.70%	13.00%
Baltimore Gas and Electric Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	5.70%	6.30%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	(0.10%)
Plant basis differences	(1.20%)	(0.90%)
Production tax credits and other credits	(0.20%)	0.00%
Noncontrolling interests	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%
Excess deferred tax amortization	(7.30%)	(7.90%)
Other	0.60%	0.00%
Effective income tax rate	18.50%	18.40%
Pepco Holdings LLC [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	5.80%	4.70%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	(0.20%)
Plant basis differences	(1.40%)	(1.70%)
Production tax credits and other credits	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%
Excess deferred tax amortization	(15.50%)	(19.40%)
Other	(0.60%)	(0.30%)
Effective income tax rate	9.20%	4.10%
Potomac Electric Power Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	4.70%	2.10%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	0.00%	(0.10%)
Plant basis differences	(2.10%)	(2.00%)
Production tax credits and other credits	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%
Excess deferred tax amortization	(14.20%)	(17.90%)
Other	(0.60%)	0.40%
Effective income tax rate	8.80%	3.50%
Delmarva Power and Light Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	6.60%	6.50%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.20%)	(0.20%)
Plant basis differences	(0.70%)	(0.70%)
Production tax credits and other credits	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%
Excess deferred tax amortization	(12.70%)	(15.60%)
Other	(0.50%)	0.70%
Effective income tax rate	13.50%	11.70%
Atlantic City Electric Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	21.00%	21.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	6.70%	6.70%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.20%)	(0.30%)
Plant basis differences	(0.80%)	(2.30%)
Production tax credits and other credits	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%
Excess deferred tax amortization	(18.80%)	(23.90%)
Other	(0.80%)	(1.20%)
Effective income tax rate	7.10%	0.00%