Income Taxes - Reconciliation to Effective Tax Rate (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate [Line Items]
U.S. Federal statutory rate	21.00%	21.00%	35.00%
State income taxes, net of Federal income tax benefit	5.40%	0.50%	2.20%
Qualified nuclear decommissioning trust fund income	5.90%	(1.90%)	3.80%
Amortization of investment tax credit, including deferred taxes on basis difference	(1.50%)	(1.20%)	(0.90%)
Plant basis differences	(1.40%)	(3.50%)	(1.70%)
Production tax credits and other credits	(3.10%)	(2.20%)	(1.80%)
Noncontrolling interests	(0.60%)	(1.00%)
Excess deferred tax amortization	(5.50%)	(8.30%)
Like-king exchange			(1.20%)
Merger expenses			(3.60%)
FitzPatrick bargain purchase gain			(2.20%)
Tax Cuts and Jobs Act of 2017		0.90%	(33.10%)
Other	(0.80%)	1.00%	0.20%
Effective income tax rate	19.40%	5.30%	(3.30%)
Amount of Impairment to Carrying Amount of Regulatory Assets		$ 35
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%	35.00%
State income taxes, net of Federal income tax benefit	3.80%	(16.60%)	2.90%
Qualified nuclear decommissioning trust fund income	12.30%	(11.80%)	9.90%
Amortization of investment tax credit, including deferred taxes on basis difference	(3.00%)	(6.50%)	(2.10%)
Plant basis differences	0.00%	0.00%	0.00%
Production tax credits and other credits	(4.80%)	(13.50%)	(4.70%)
Noncontrolling interests	(1.20%)	(6.10%)
Excess deferred tax amortization	0.00%	0.00%
Like-king exchange			0.00%
Merger expenses			(1.20%)
FitzPatrick bargain purchase gain			(5.60%)
Tax Cuts and Jobs Act of 2017		2.70%	(128.30%)
Other	(1.20%)	1.30%	(0.50%)
Effective income tax rate	26.90%	(29.50%)	(94.60%)
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%	35.00%
State income taxes, net of Federal income tax benefit	8.50%	8.30%	5.70%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.20%)	(0.20%)	(0.20%)
Plant basis differences	0.00%	(0.20%)	0.30%
Production tax credits and other credits	(1.20%)	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%
Excess deferred tax amortization	(9.70%)	(9.10%)
Like-king exchange			1.30%
Merger expenses			0.00%
FitzPatrick bargain purchase gain			0.00%
Tax Cuts and Jobs Act of 2017		(0.10%)	0.10%
Other	0.80%	0.50%	0.20%
Effective income tax rate	19.20%	20.20%	42.40%
Amount of Impairment to Carrying Amount of Regulatory Assets		$ 3
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%	35.00%
State income taxes, net of Federal income tax benefit	0.00%	(2.60%)	0.60%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	0.00%	(0.10%)	(0.10%)
Plant basis differences	(7.20%)	(14.10%)	(13.80%)
Production tax credits and other credits	0.00%	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%
Excess deferred tax amortization	(2.80%)	(3.20%)
Like-king exchange			0.00%
Merger expenses			0.00%
FitzPatrick bargain purchase gain			0.00%
Tax Cuts and Jobs Act of 2017		0.00%	(2.30%)
Other	0.00%	0.30%	(0.10%)
Effective income tax rate	11.00%	1.30%	19.30%
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%	35.00%
State income taxes, net of Federal income tax benefit	6.40%	6.60%	5.40%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	(0.10%)	(0.10%)
Plant basis differences	(1.20%)	(1.30%)	0.10%
Production tax credits and other credits	(1.30%)	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%
Excess deferred tax amortization	(6.80%)	(8.00%)
Like-king exchange			0.00%
Merger expenses			0.00%
FitzPatrick bargain purchase gain			0.00%
Tax Cuts and Jobs Act of 2017		0.00%	0.90%
Other	0.00%	0.90%	0.20%
Effective income tax rate	18.00%	19.10%	41.50%
Amount of Impairment to Carrying Amount of Regulatory Assets		$ 5
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%	35.00%
State income taxes, net of Federal income tax benefit	4.70%	2.90%	4.80%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.20%)	(0.20%)	(0.20%)
Plant basis differences	(1.20%)	(1.60%)	1.10%
Production tax credits and other credits	(0.20%)	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%
Excess deferred tax amortization	(17.50%)	(14.80%)
Like-king exchange			0.00%
Merger expenses			(9.60%)
FitzPatrick bargain purchase gain			0.00%
Tax Cuts and Jobs Act of 2017		0.10%	6.40%
Other	0.80%	0.40%	0.50%
Effective income tax rate	7.40%	7.80%	38.00%
Amount of Impairment to Carrying Amount of Regulatory Assets		$ 27
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%	35.00%
State income taxes, net of Federal income tax benefit	2.00%	2.00%	3.10%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.10%)	(0.10%)	(0.10%)
Plant basis differences	(1.80%)	(2.80%)	(0.40%)
Production tax credits and other credits	(0.10%)	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%
Excess deferred tax amortization	(15.10%)	(15.30%)
Like-king exchange			0.00%
Merger expenses			(6.40%)
FitzPatrick bargain purchase gain			0.00%
Tax Cuts and Jobs Act of 2017		0.00%	2.80%
Other	0.30%	0.30%	0.70%
Effective income tax rate	6.20%	5.10%	34.70%
Amount of Impairment to Carrying Amount of Regulatory Assets		$ 14
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%	35.00%
State income taxes, net of Federal income tax benefit	6.80%	6.70%	5.40%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.20%)	(0.30%)	(0.20%)
Plant basis differences	(0.40%)	(0.30%)	2.00%
Production tax credits and other credits	0.00%	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%
Excess deferred tax amortization	(14.20%)	(12.00%)
Like-king exchange			0.00%
Merger expenses			(7.80%)
FitzPatrick bargain purchase gain			0.00%
Tax Cuts and Jobs Act of 2017		0.00%	2.50%
Other	0.00%	0.40%	0.10%
Effective income tax rate	13.00%	15.50%	37.00%
Amount of Impairment to Carrying Amount of Regulatory Assets		$ 6
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%	35.00%
State income taxes, net of Federal income tax benefit	7.00%	7.40%	5.60%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%	0.00%
Amortization of investment tax credit, including deferred taxes on basis difference	(0.30%)	(0.40%)	(0.40%)
Plant basis differences	(0.70%)	(0.50%)	3.60%
Production tax credits and other credits	(0.10%)	0.00%	0.00%
Noncontrolling interests	0.00%	0.00%
Excess deferred tax amortization	(27.00%)	(14.90%)
Like-king exchange			0.00%
Merger expenses			(19.80%)
FitzPatrick bargain purchase gain			0.00%
Tax Cuts and Jobs Act of 2017		0.00%	1.60%
Other	0.10%	1.20%	(0.40%)
Effective income tax rate	0.00%	13.80%	25.20%
Amount of Impairment to Carrying Amount of Regulatory Assets		$ 7