Income Taxes - Reconciliation to Effective Tax Rate (Details)	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
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	12.30%	6.40%	9.30%	5.10%
Qualified nuclear decommissioning trust fund income	13.20%	3.20%	3.20%	5.30%
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments			2.50%
Amortization of investment tax credit, including deferred taxes on basis difference	(1.40%)	(4.10%)	(1.20%)	(1.90%)
Plant basis differences	(4.30%)	(1.70%)	(4.00%)	(1.60%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	(3.00%)	(1.20%)	(2.60%)	(1.00%)
Noncontrolling interests	0.80%	(2.20%)	1.00%	(1.00%)
Excess deferred tax amortization	(10.10%)	(6.50%)	(15.80%)	(6.00%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	(0.20%)		(5.00%)
Other	(0.80%)	0.70%	0.10%	0.80%
Effective income tax rate	27.50%	15.60%	8.50%	20.70%
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	(10.30%)	5.20%	0.00%	4.20%
Qualified nuclear decommissioning trust fund income	47.40%	7.10%	10.00%	11.90%
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments			0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(4.50%)	(8.90%)	(3.20%)	(4.00%)
Plant basis differences	0.00%	0.00%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	(9.20%)	(2.70%)	(7.00%)	(2.10%)
Noncontrolling interests	2.90%	(4.80%)	3.10%	(2.30%)
Excess deferred tax amortization	0.00%	0.00%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	(0.70%)		(15.70%)
Other	(0.90%)	0.50%	(0.50%)	(0.10%)
Effective income tax rate	45.70%	17.40%	7.70%	28.60%
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%	8.10%	12.70%	8.20%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments			9.40%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.20%)	(0.20%)	(0.30%)	(0.20%)
Plant basis differences	(0.60%)	(1.00%)	(0.90%)	(0.70%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	(0.40%)	0.00%	(0.40%)	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(5.60%)	(9.90%)	(11.80%)	(9.20%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%		0.00%
Other	1.10%	0.40%	2.10%	0.20%
Effective income tax rate	23.40%	18.40%	31.80%	19.30%
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	(6.20%)	(0.30%)	(3.40%)	0.00%
Qualified nuclear decommissioning trust fund income	0.00%	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%	0.00%	0.00%
Plant basis differences	(23.30%)	(7.50%)	(15.90%)	(6.80%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	0.00%	0.00%	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(3.80%)	(3.60%)	(3.50%)	(2.90%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%		0.00%
Other	(0.80%)	(0.50%)	(0.50%)	(0.20%)
Effective income tax rate	(13.10%)	9.10%	(2.30%)	11.10%
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	5.10%	6.30%	5.50%	6.40%
Qualified nuclear decommissioning trust fund income	0.00%	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%)	(0.10%)
Plant basis differences	(1.20%)	(1.10%)	(1.80%)	(1.10%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	(0.80%)	0.00%	(0.40%)	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(10.60%)	(8.00%)	(15.00%)	(7.90%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%		0.00%
Other	(0.30%)	(0.20%)	(0.50%)	0.10%
Effective income tax rate	13.10%	17.90%	8.70%	18.40%
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	5.50%	4.80%	5.00%	4.80%
Qualified nuclear decommissioning trust fund income	0.00%	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%)	(0.20%)
Plant basis differences	(1.50%)	(1.80%)	(2.20%)	(1.80%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	(0.50%)	0.00%	(0.30%)	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(24.90%)	(17.70%)	(45.30%)	(18.60%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%		0.00%
Other	0.10%	0.80%	(0.60%)	0.50%
Effective income tax rate	(0.50%)	6.90%	(22.60%)	5.70%
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	4.60%	1.90%	4.20%	2.00%
Qualified nuclear decommissioning trust fund income	0.00%	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%)	(0.10%)
Plant basis differences	(2.10%)	(2.60%)	(2.40%)	(2.30%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	(0.50%)	0.00%	(0.30%)	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(20.00%)	(16.30%)	(29.20%)	(17.30%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%		0.00%
Other	(0.40%)	1.00%	(0.80%)	0.70%
Effective income tax rate	2.50%	4.90%	(7.60%)	4.00%
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%	6.50%	6.70%
Qualified nuclear decommissioning trust fund income	0.00%	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%)	(0.30%)	(0.20%)
Plant basis differences	(0.40%)	(0.60%)	(0.50%)	(0.60%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	(0.50%)	0.00%	(0.20%)	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(23.60%)	(13.50%)	(53.60%)	(15.00%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%		0.00%
Other	0.70%	(0.10%)	(1.10%)	0.20%
Effective income tax rate	3.60%	13.20%	(28.20%)	12.10%
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%	6.90%	6.80%	6.90%
Qualified nuclear decommissioning trust fund income	0.00%	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%)	(0.30%)	(0.50%)	(0.30%)
Plant basis differences	(1.30%)	(1.90%)	(3.70%)	(2.00%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent	(0.40%)	0.00%	(0.40%)	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(36.80%)	(23.30%)	(81.40%)	(23.40%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%		0.00%
Other	0.60%	0.70%	0.00%	0.00%
Effective income tax rate	(10.30%)	3.10%	(58.20%)	2.20%

Adjustments to reconcile the domestic federal statutory tax rate to a company's effective income tax rate abstract.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to change in enacted tax law, excluding changes in the income tax rates.

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to qualified decommissioning investment income taxes paid.

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to income tax settlements. Including, but not limited to, domestic tax settlement, foreign tax settlement, state and local tax settlement, and other tax settlements.

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