Income Taxes - Reconciliation to Effective Tax Rate (Details)	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 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	3.80%	5.40%	6.70%	4.40%
Qualified nuclear decommissioning trust fund income	18.80%	5.10%	(5.70%)	6.50%
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments	5.30%		4.80%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.60%)	(0.70%)	(1.00%)	(0.60%)
Plant basis differences	(1.60%)	(1.70%)	(3.70%)	(1.50%)
Production tax credits and other credits	1.40%	0.90%	2.20%	0.80%
Noncontrolling interests	0.10%	0.10%	1.10%	(0.30%)
Excess deferred tax amortization	(15.50%)	(7.80%)	(20.90%)	(5.80%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	(1.90%)		(9.30%)
Other	(0.40%)	1.90%	0.70%	0.70%
Effective income tax rate	27.60%	22.40%	(8.50%)	23.60%
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	3.10%	5.50%	7.20%	3.60%
Qualified nuclear decommissioning trust fund income	17.30%	16.20%	(16.00%)	14.70%
Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments	0.00%		0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.50%)	(1.90%)	(2.30%)	(1.10%)
Plant basis differences	0.00%	0.00%	0.00%	0.00%
Production tax credits and other credits	1.20%	2.80%	5.50%	1.80%
Noncontrolling interests	0.10%	0.40%	3.20%	(0.80%)
Excess deferred tax amortization	0.00%	0.00%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	(1.80%)		(26.10%)
Other	0.30%	0.20%	(0.30%)	(0.40%)
Effective income tax rate	38.30%	38.60%	(18.80%)	35.20%
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	(131.70%)	8.20%	19.10%	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	(288.30%)		22.20%
Amortization of investment tax credit, including deferred taxes on basis difference	2.90%	(0.20%)	(0.40%)	(0.20%)
Plant basis differences	2.40%	(0.60%)	(1.40%)	(0.60%)
Production tax credits and other credits	(3.30%)	0.00%	0.40%	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	116.00%	(9.00%)	(20.20%)	(8.80%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%		0.00%
Other	(32.30%)	0.40%	3.50%	0.20%
Effective income tax rate	(306.70%)	19.80%	43.40%	19.80%
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	(9.70%)	(1.20%)	(1.60%)	0.20%
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%		0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	0.00%	0.00%	0.00%	0.00%
Plant basis differences	(23.60%)	(5.90%)	(11.00%)	(6.40%)
Production tax credits and other credits	0.00%	0.00%	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(4.80%)	(2.70%)	(3.30%)	(2.60%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%		0.00%
Other	(4.80%)	0.10%	(0.30%)	(0.10%)
Effective income tax rate	(21.90%)	11.30%	4.80%	12.10%
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	3.80%	6.50%	5.60%	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%		0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.20%)	(0.10%)	(0.10%)	(0.10%)
Plant basis differences	(13.40%)	(1.50%)	(2.00%)	(1.00%)
Production tax credits and other credits	1.00%	0.10%	0.20%	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(137.90%)	(7.90%)	(16.10%)	(7.90%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%		0.00%
Other	(1.70%)	1.70%	(0.60%)	0.20%
Effective income tax rate	(129.40%)	19.60%	7.60%	18.60%
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	(25.80%)	4.80%	4.30%	4.70%
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%		0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(2.20%)	(0.20%)	(0.20%)	(0.20%)
Plant basis differences	(44.70%)	(1.70%)	(3.50%)	(1.70%)
Production tax credits and other credits	0.70%	0.00%	0.10%	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(1358.50%)	(19.40%)	(80.30%)	(19.40%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%		0.00%
Other	168.00%	0.90%	(1.50%)	0.30%
Effective income tax rate	(1242.90%)	5.40%	(60.30%)	4.70%
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	2.10%	2.00%	3.70%	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%		0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	(0.10%)	(0.10%)	(0.10%)
Plant basis differences	(3.90%)	(2.10%)	(2.70%)	(2.00%)
Production tax credits and other credits	0.10%	0.00%	0.10%	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	(89.00%)	(18.30%)	(41.60%)	(18.10%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%		0.00%
Other	(2.70%)	0.50%	(1.30%)	0.50%
Effective income tax rate	(72.70%)	3.00%	(21.10%)	3.30%
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	6.70%	7.00%	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%		0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	0.50%	(0.20%)	(0.30%)	(0.20%)
Plant basis differences	(1.10%)	(0.30%)	(0.60%)	(0.60%)
Production tax credits and other credits	(0.10%)	0.00%	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	284.00%	(15.70%)	(72.90%)	(15.60%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%		0.00%
Other	(0.10%)	0.00%	0.80%	0.40%
Effective income tax rate	311.10%	11.80%	(45.50%)	11.70%
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	7.20%	7.00%	12.40%	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%		0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	0.30%	(0.30%)	7.20%	(0.30%)
Plant basis differences	10.00%	(2.20%)	146.20%	(2.20%)
Production tax credits and other credits	0.00%	0.00%	(0.70%)	0.00%
Noncontrolling interests	0.00%	0.00%	0.00%	0.00%
Excess deferred tax amortization	174.50%	(23.10%)	2613.80%	(23.40%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent	0.00%		0.00%
Other	7.00%	(2.40%)	398.70%	2.00%
Effective income tax rate	220.00%	0.00%	3200.00%	4.00%

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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Effective Income Tax Rate Reconciliation, Deferred Prosecution Agreement payments

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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 noncontrolling interest income (loss) exempt from income taxes.

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