Income Taxes - Reconciliation to Effective Tax Rate (Details)		3 Months Ended			9 Months Ended			12 Months Ended
		Sep. 30, 2018	Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017		Dec. 31, 2017
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%	[1]	21.00%	35.00%	[1]	35.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		(1.20%)	2.20%	[1]	1.70%	0.70%	[1]
Qualified nuclear decommissioning trust fund income		2.40%	2.60%	[1]	0.90%	4.00%	[1]
Amortization of investment tax credit, including deferred taxes on basis difference		(0.60%)	(1.10%)	[1]	(0.90%)	(0.90%)	[1]
Plant basis differences		(2.50%)	(2.60%)	[1]	(2.70%)	(3.40%)	[1]
Production tax credits and other credits		(1.20%)	(2.20%)	[1]	(1.80%)	(1.80%)	[1]
Noncontrolling interests		(1.10%)	0.50%	[1]	(1.10%)	0.10%	[1]
Excess deferred tax amortization		(6.80%)			(6.10%)
Merger expenses	[1],[2]					(5.40%)
FitzPatrick bargain purchase gain	[1]		(0.20%)			(3.20%)
Tax Cuts and Jobs Act of 2017		1.30%			0.20%
Like-Kind Exchange	[1],[3]					(1.70%)
Other		3.20%	(0.10%)	[1]	0.40%	0.10%	[1]
Effective income tax rate		14.50%	34.10%		11.60%	23.50%
Exelon Generation Co L L C [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%	[1]	21.00%	35.00%	[1]
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		(9.00%)	5.60%	[1]	(2.60%)	2.20%	[1]
Qualified nuclear decommissioning trust fund income		5.80%	5.80%	[1]	2.60%	13.60%	[1]
Amortization of investment tax credit, including deferred taxes on basis difference		(1.10%)	(2.20%)	[1]	(2.20%)	(2.70%)	[1]
Plant basis differences		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Production tax credits and other credits		(2.90%)	(4.90%)	[1]	(5.10%)	(6.00%)	[1]
Noncontrolling interests		(2.80%)	1.10%	[1]	(3.20%)	0.30%	[1]
Excess deferred tax amortization		0.00%			0.00%
Merger expenses	[1],[2]					(2.40%)
FitzPatrick bargain purchase gain	[1]		(0.40%)			(10.90%)
Tax Cuts and Jobs Act of 2017		3.50%			1.30%
Like-Kind Exchange	[1]					0.00%
Other		5.60%	0.30%	[1]	2.00%	(0.40%)	[1]
Effective income tax rate		20.10%	40.30%		13.80%	28.70%
Commonwealth Edison Co [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%	[1]	21.00%	35.00%	[1]
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		8.30%	6.60%	[1]	8.20%	5.90%	[1]
Qualified nuclear decommissioning trust fund income		0.00%	0.00%	[1]	0.00%	0.00%	[1]
Amortization of investment tax credit, including deferred taxes on basis difference		(0.20%)	(0.20%)	[1]	(0.20%)	(0.20%)	[1]
Plant basis differences		(0.30%)	(0.30%)	[1]	(0.10%)	(0.30%)	[1]
Production tax credits and other credits		(0.10%)	(0.00%)	[1]	(0.10%)	(0.00%)	[1]
Noncontrolling interests		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Excess deferred tax amortization		(7.80%)			(7.60%)
Merger expenses	[1],[2]					0.00%
FitzPatrick bargain purchase gain	[1]		0.00%			0.00%
Tax Cuts and Jobs Act of 2017		0.00%			(0.20%)
Like-Kind Exchange	[1],[3]					1.70%
Other		0.30%	(0.20%)	[1]	0.10%	0.20%	[1]
Effective income tax rate		21.20%	40.90%		21.10%	42.30%
PECO Energy Co [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%	[1]	21.00%	35.00%	[1]
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		(3.60%)	(0.10%)	[1]	(3.60%)	(0.10%)	[1]
Qualified nuclear decommissioning trust fund income		0.00%	0.00%	[1]	0.00%	0.00%	[1]
Amortization of investment tax credit, including deferred taxes on basis difference		(0.10%)	(0.10%)	[1]	(0.10%)	(0.10%)	[1]
Plant basis differences		(15.20%)	(14.60%)	[1]	(15.40%)	(14.40%)	[1]
Production tax credits and other credits		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Noncontrolling interests		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Excess deferred tax amortization		(4.60%)			(3.40%)
Merger expenses	[1],[2]					0.00%
FitzPatrick bargain purchase gain	[1]		0.00%			0.00%
Tax Cuts and Jobs Act of 2017		0.00%			0.00%
Like-Kind Exchange	[1]					0.00%
Other		0.90%	(0.20%)	[1]	0.00%	0.00%	[1]
Effective income tax rate		(1.60%)	20.00%		(1.50%)	20.40%
Baltimore Gas and Electric Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%	[1]	21.00%	35.00%	[1]
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		7.30%	5.30%	[1]	6.60%	5.20%	[1]
Qualified nuclear decommissioning trust fund income		0.00%	0.00%	[1]	0.00%	0.00%	[1]
Amortization of investment tax credit, including deferred taxes on basis difference		(0.00%)	(0.10%)	[1]	(0.10%)	(0.10%)	[1]
Plant basis differences		(0.80%)	(0.80%)	[1]	(0.70%)	(0.80%)	[1]
Production tax credits and other credits		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Noncontrolling interests		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Excess deferred tax amortization		(7.90%)			(8.10%)
Merger expenses	[1],[2]					0.00%
FitzPatrick bargain purchase gain	[1]		0.00%			0.00%
Tax Cuts and Jobs Act of 2017		0.00%			0.00%
Like-Kind Exchange	[1]					0.00%
Other		2.60%	(0.20%)	[1]	0.90%	0.20%	[1]
Effective income tax rate		22.20%	39.20%		19.60%	39.50%
Pepco Holdings LLC [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%	[1]	21.00%	35.00%	[1]
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		0.20%	5.10%	[1]	2.70%	4.90%	[1]
Qualified nuclear decommissioning trust fund income		0.00%	0.00%	[1]	0.00%	0.00%	[1]
Amortization of investment tax credit, including deferred taxes on basis difference		(0.20%)	(0.20%)	[1]	(0.20%)	(0.20%)	[1]
Plant basis differences		(2.00%)	(4.90%)	[1]	(1.90%)	(4.60%)	[1]
Production tax credits and other credits		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Noncontrolling interests		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Excess deferred tax amortization		(17.70%)			(14.50%)
Merger expenses	[1],[2]					(11.80%)
FitzPatrick bargain purchase gain	[1]		0.00%			0.00%
Tax Cuts and Jobs Act of 2017		0.20%			0.30%
Like-Kind Exchange	[1]					0.00%
Other		0.60%	0.20%	[1]	0.30%	0.00%	[1]
Effective income tax rate		2.10%	35.20%		7.70%	23.30%
Potomac Electric Power Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%	[1]	21.00%	35.00%	[1]
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		1.00%	2.20%	[1]	2.40%	3.00%	[1]
Qualified nuclear decommissioning trust fund income		0.00%	0.00%	[1]	0.00%	0.00%	[1]
Amortization of investment tax credit, including deferred taxes on basis difference		(0.10%)	(0.10%)	[1]	(0.10%)	(0.10%)	[1]
Plant basis differences		(3.40%)	(6.70%)	[1]	(2.90%)	(6.30%)	[1]
Production tax credits and other credits		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Noncontrolling interests		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Excess deferred tax amortization		(21.20%)			(16.50%)
Merger expenses	[1],[2]					(8.00%)
FitzPatrick bargain purchase gain	[1]		0.00%			0.00%
Tax Cuts and Jobs Act of 2017		0.10%			0.00%
Like-Kind Exchange	[1]					0.00%
Other		0.30%	0.00%	[1]	0.00%	(0.30%)	[1]
Effective income tax rate		(2.30%)	30.40%		3.90%	23.30%
Delmarva Power and Light Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%	[1]	21.00%	35.00%	[1]
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		6.60%	5.30%	[1]	6.50%	5.10%	[1]
Qualified nuclear decommissioning trust fund income		0.00%	0.00%	[1]	0.00%	0.00%	[1]
Amortization of investment tax credit, including deferred taxes on basis difference		(0.30%)	(0.20%)	[1]	(0.30%)	(0.20%)	[1]
Plant basis differences		(0.70%)	(1.90%)	[1]	(0.70%)	(1.80%)	[1]
Production tax credits and other credits		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Noncontrolling interests		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Excess deferred tax amortization		(14.00%)			(11.00%)
Merger expenses	[1],[2]					(10.00%)
FitzPatrick bargain purchase gain	[1]		0.00%			0.00%
Tax Cuts and Jobs Act of 2017		0.00%			0.00%
Like-Kind Exchange	[1]					0.00%
Other		0.60%	(0.20%)	[1]	0.40%	0.60%	[1]
Effective income tax rate		13.20%	38.00%		15.90%	28.70%
Atlantic City Electric Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate		21.00%	35.00%	[1]	21.00%	35.00%	[1]
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit		7.30%	5.60%	[1]	7.30%	5.60%	[1]
Qualified nuclear decommissioning trust fund income		0.00%	0.00%	[1]	0.00%	0.00%	[1]
Amortization of investment tax credit, including deferred taxes on basis difference		(0.30%)	(0.40%)	[1]	(0.30%)	(0.40%)	[1]
Plant basis differences		(1.30%)	(3.40%)	[1]	(1.30%)	(3.40%)	[1]
Production tax credits and other credits		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Noncontrolling interests		(0.00%)	(0.00%)	[1]	(0.00%)	(0.00%)	[1]
Excess deferred tax amortization		(15.40%)			(14.00%)
Merger expenses	[1],[2]					(23.00%)
FitzPatrick bargain purchase gain	[1]		0.00%			0.00%
Tax Cuts and Jobs Act of 2017		0.00%			0.00%
Like-Kind Exchange	[1]					0.00%
Other		0.30%	0.10%	[1]	0.90%	(0.30%)	[1]
Effective income tax rate		11.60%	36.90%		13.60%	13.50%

[1] Exelon retrospectively adopted the new standard Revenue from Contracts with Customers. The standard was adopted as of January 1, 2018. The effective income tax rates are recast to reflect the impact of the new standard.

[2] Includes a remeasurement of uncertain federal and state income tax positions.

[3] Exelon and ComEd recorded the impact of the IRS's finalization of the LKE computation in the second quarter of 2017