Income Taxes - Reconciliation to Effective Tax Rate (Details)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
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	14.60%	34.00%
Qualified nuclear decommissioning trust fund income	(18.40%)	(235.80%)
Amortization of investment tax credit, including deferred taxes on basis difference	2.40%	(4.50%)
Plant basis differences	8.80%	(23.00%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	6.70%	(9.90%)
Noncontrolling interests	0.60%	10.60%
Excess deferred tax amortization	27.90%	(71.70%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent		(79.10%)
Other	(56.90%)	12.50%
Effective income tax rate	6.70%	(345.90%)
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	4.40%	0.70%
Qualified nuclear decommissioning trust fund income	(5.50%)	36.40%
Amortization of investment tax credit, including deferred taxes on basis difference	0.60%	0.50%
Plant basis differences	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	1.80%	1.30%
Noncontrolling interests	0.20%	(1.60%)
Excess deferred tax amortization	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent		12.20%
Other	(3.60%)	0.60%
Effective income tax rate	18.90%	71.10%
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	6.80%	8.30%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	(0.20%)
Plant basis differences	(0.60%)	(1.10%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	(0.20%)	(0.20%)
Noncontrolling interests	0.00%	0.00%
Excess deferred tax amortization	(6.90%)	(10.50%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent		0.00%
Other	(3.50%)	0.30%
Effective income tax rate	16.50%	17.60%
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	(1.60%)	0.10%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	0.00%	0.00%
Plant basis differences	(10.50%)	(8.40%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%
Excess deferred tax amortization	(3.20%)	(3.00%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent		0.00%
Other	(0.10%)	0.00%
Effective income tax rate	5.60%	9.70%
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	(10.10%)	5.70%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	(0.10%)
Plant basis differences	(1.40%)	(1.20%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	(0.40%)	(0.20%)
Noncontrolling interests	0.00%	0.00%
Excess deferred tax amortization	(15.50%)	(7.30%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent		0.00%
Other	(0.10%)	0.60%
Effective income tax rate	(6.60%)	18.50%
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	6.10%	5.80%
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	(1.50%)	(1.40%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	(0.20%)	0.00%
Noncontrolling interests	0.00%	0.00%
Excess deferred tax amortization	(19.30%)	(15.50%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent		0.00%
Other	(0.10%)	(0.60%)
Effective income tax rate	5.90%	9.20%
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	5.50%	4.70%
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	(2.10%)	(2.10%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	(0.20%)	0.00%
Noncontrolling interests	0.00%	0.00%
Excess deferred tax amortization	(15.10%)	(14.20%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent		0.00%
Other	0.10%	(0.60%)
Effective income tax rate	9.20%	8.80%
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	6.40%	6.60%
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%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	(0.10%)	0.00%
Noncontrolling interests	0.00%	0.00%
Excess deferred tax amortization	(18.50%)	(12.70%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent		0.00%
Other	0.30%	(0.50%)
Effective income tax rate	8.20%	13.50%
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	6.90%	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%)	(0.20%)
Plant basis differences	(0.90%)	(0.80%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	(0.30%)	0.00%
Noncontrolling interests	0.00%	0.00%
Excess deferred tax amortization	(28.70%)	(18.80%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent		0.00%
Other	2.20%	(0.80%)
Effective income tax rate	0.00%	7.10%