Income Taxes - Reconciliation to Effective Tax Rate (Details)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
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	3.90%	4.10%
Qualified nuclear decommissioning trust fund income	7.20%	(0.40%)
Amortization of investment tax credit, including deferred taxes on basis difference	(0.50%)	(1.30%)
Plant basis differences	(1.40%)	(2.70%)
Production tax credits and other credits	(0.80%)	(2.80%)
Noncontrolling interests	(0.60%)	(0.70%)
Excess deferred tax amortization	(4.70%)	(6.00%)
Other	0.10%	(2.80%)
Effective income tax rate	24.20%	8.40%
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	3.10%	2.40%
Qualified nuclear decommissioning trust fund income	14.20%	(1.30%)
Amortization of investment tax credit, including deferred taxes on basis difference	(0.90%)	(4.30%)
Plant basis differences	(0.00%)	(0.00%)
Production tax credits and other credits	(1.50%)	(9.50%)
Noncontrolling interests	(1.10%)	(2.50%)
Excess deferred tax amortization	0.00%	0.00%
Other	(0.50%)	(1.30%)
Effective income tax rate	34.30%	4.50%
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	8.20%	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	(0.50%)	0.10%
Production tax credits and other credits	(0.00%)	(0.10%)
Noncontrolling interests	(0.00%)	(0.00%)
Excess deferred tax amortization	(8.50%)	(7.50%)
Other	0.30%	0.30%
Effective income tax rate	20.30%	21.80%
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	1.00%	(3.90%)
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	(6.70%)	(14.20%)
Production tax credits and other credits	(0.00%)	(0.00%)
Noncontrolling interests	(0.00%)	(0.00%)
Excess deferred tax amortization	(2.50%)	(4.80%)
Other	0.20%	0.20%
Effective income tax rate	13.00%	(1.80%)
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	6.30%	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	(0.90%)	(0.70%)
Production tax credits and other credits	(0.00%)	(0.00%)
Noncontrolling interests	(0.00%)	(0.00%)
Excess deferred tax amortization	(7.90%)	(8.60%)
Other	0.00%	0.00%
Effective income tax rate	18.40%	17.90%
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	4.70%	4.60%
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	(1.70%)	(2.60%)
Production tax credits and other credits	(0.00%)	(0.00%)
Noncontrolling interests	(0.00%)	(0.00%)
Excess deferred tax amortization	(19.40%)	(10.60%)
Other	(0.30%)	0.00%
Effective income tax rate	4.10%	12.20%
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	2.10%	1.70%
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	(2.00%)	(3.40%)
Production tax credits and other credits	(0.00%)	(0.00%)
Noncontrolling interests	(0.00%)	(0.00%)
Excess deferred tax amortization	(17.90%)	(12.80%)
Other	0.40%	(0.30%)
Effective income tax rate	3.50%	6.10%
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	6.50%	6.30%
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%)	(1.30%)
Production tax credits and other credits	(0.00%)	(0.00%)
Noncontrolling interests	(0.00%)	(0.00%)
Excess deferred tax amortization	(15.60%)	(7.90%)
Other	0.70%	0.50%
Effective income tax rate	11.70%	18.40%
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%	6.60%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.30%)	(0.30%)
Plant basis differences	(2.30%)	(2.60%)
Production tax credits and other credits	(0.00%)	(0.00%)
Noncontrolling interests	(0.00%)	(0.00%)
Excess deferred tax amortization	(23.90%)	(8.70%)
Other	(1.20%)	(3.50%)
Effective income tax rate	0.00%	12.50%