Income Taxes - Reconciliation to Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate	21.00%	21.00%	21.00%
State income taxes, net of Federal income tax benefit	7.80%	5.40%	0.50%
Qualified nuclear decommissioning trust fund income	8.40%	5.90%	(1.90%)
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments	1.80%
Amortization of investment tax credit, including deferred taxes on basis difference	(1.10%)	(1.50%)	(1.20%)
Plant basis differences	(4.00%)	(1.40%)	(3.50%)
Production tax credits and other credits	(2.20%)	(3.10%)	(2.20%)
Noncontrolling interests	1.10%	(0.60%)	(1.00%)
Excess deferred tax amortization	(13.60%)	(5.50%)	(8.30%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	(3.70%)
Tax Cuts and Jobs Act of 2017			0.90%
Other	0.50%	(0.80%)	1.00%
Effective income tax rate	16.00%	19.40%	5.30%
Exelon Generation Co L L C [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate	21.00%	21.00%	21.00%
State income taxes, net of Federal income tax benefit	0.50%	3.80%	(16.60%)
Qualified nuclear decommissioning trust fund income	23.50%	12.30%	(11.80%)
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(2.60%)	(3.00%)	(6.50%)
Plant basis differences	0.00%	0.00%	0.00%
Production tax credits and other credits	(5.40%)	(4.80%)	(13.50%)
Noncontrolling interests	3.20%	(1.20%)	(6.10%)
Excess deferred tax amortization	0.00%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	(10.30%)
Tax Cuts and Jobs Act of 2017			2.70%
Other	(0.10%)	(1.20%)	1.30%
Effective income tax rate	29.80%	26.90%	(29.50%)
Commonwealth Edison Co [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate	21.00%	21.00%	21.00%
State income taxes, net of Federal income tax benefit	11.60%	8.50%	8.30%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments	6.80%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.30%)	(0.20%)	(0.20%)
Plant basis differences	(0.60%)	0.00%	(0.20%)
Production tax credits and other credits	(0.30%)	1.20%	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%
Excess deferred tax amortization	(11.20%)	(9.70%)	(9.10%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%
Tax Cuts and Jobs Act of 2017			(0.10%)
Other	1.80%	0.80%	0.50%
Effective income tax rate	28.80%	19.20%	20.20%
PECO Energy Co [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate	21.00%	21.00%	21.00%
State income taxes, net of Federal income tax benefit	(4.50%)	0.00%	(2.60%)
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	0.00%	0.00%	(0.10%)
Plant basis differences	(18.70%)	(7.20%)	(14.10%)
Production tax credits and other credits	0.00%	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%
Excess deferred tax amortization	(4.60%)	(2.80%)	(3.20%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%
Tax Cuts and Jobs Act of 2017			0.00%
Other	(0.40%)	0.00%	0.30%
Effective income tax rate	(7.20%)	11.00%	1.30%
Baltimore Gas and Electric Company [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate	21.00%	21.00%	21.00%
State income taxes, net of Federal income tax benefit	5.50%	6.40%	6.60%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	(0.10%)	(0.10%)
Plant basis differences	(1.50%)	(1.20%)	(1.30%)
Production tax credits and other credits	(0.40%)	1.30%	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%
Excess deferred tax amortization	(13.90%)	(6.80%)	(8.00%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%
Tax Cuts and Jobs Act of 2017			0.00%
Other	(0.10%)	0.00%	0.90%
Effective income tax rate	10.50%	18.00%	19.10%
Pepco Holdings LLC [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate	21.00%	21.00%	21.00%
State income taxes, net of Federal income tax benefit	5.10%	4.70%	2.90%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.20%)	(0.20%)	(0.20%)
Plant basis differences	(1.60%)	(1.20%)	(1.60%)
Production tax credits and other credits	(0.30%)	(0.20%)	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%
Excess deferred tax amortization	(42.00%)	(17.50%)	(14.80%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%
Tax Cuts and Jobs Act of 2017			0.10%
Other	(0.40%)	0.80%	0.40%
Effective income tax rate	(18.40%)	7.40%	7.80%
Potomac Electric Power Company [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate	21.00%	21.00%	21.00%
State income taxes, net of Federal income tax benefit	4.50%	2.00%	2.00%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	(0.10%)	(0.10%)
Plant basis differences	(1.70%)	(1.80%)	(2.80%)
Production tax credits and other credits	(0.30%)	0.10%	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%
Excess deferred tax amortization	(25.40%)	(15.10%)	(15.30%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%
Tax Cuts and Jobs Act of 2017			0.00%
Other	(0.70%)	0.30%	0.30%
Effective income tax rate	(2.70%)	6.20%	5.10%
Delmarva Power & Light Company [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate	21.00%	21.00%	21.00%
State income taxes, net of Federal income tax benefit	6.60%	6.80%	6.70%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.30%)	(0.20%)	(0.30%)
Plant basis differences	(0.40%)	(0.40%)	(0.30%)
Production tax credits and other credits	(0.30%)	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%
Excess deferred tax amortization	(51.70%)	(14.20%)	(12.00%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%
Tax Cuts and Jobs Act of 2017			0.00%
Other	0.10%	0.00%	0.40%
Effective income tax rate	(25.00%)	13.00%	15.50%
Atlantic City Electric Company [Member]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate	21.00%	21.00%	21.00%
State income taxes, net of Federal income tax benefit	7.00%	7.00%	7.40%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.50%)	(0.30%)	(0.40%)
Plant basis differences	(3.00%)	(0.70%)	(0.50%)
Production tax credits and other credits	(0.50%)	0.10%	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%
Excess deferred tax amortization	(82.10%)	(27.00%)	(14.90%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%
Tax Cuts and Jobs Act of 2017			0.00%
Other	0.40%	0.10%	1.20%
Effective income tax rate	(57.70%)	0.00%	13.80%