Income Taxes - Reconciliation to Effective Tax Rate (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended		12 Months Ended
		Mar. 23, 2016		Dec. 31, 2016	[7]	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Income Taxes [Line Items]
U.S. Federal statutory rate						21.00%	35.00%		35.00%		35.00%
State income taxes, net of Federal income tax benefit (d)							2.30%		3.30%	[1]	3.70%
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Percent							3.80%		(3.40%)		0.40%
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Percent											(0.70%)
Effective Income Tax Rate Reconciliation, Deduction, Medicare Prescription Drug Benefit, Percent											(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference							(0.90%)		(1.20%)		0.90%
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent							(1.70%)		(4.80%)		(1.50%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent							(1.80%)		(3.60%)		(1.90%)
Noncontrolling interests							0.10%		0.20%		0.30%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent							(1.20%)		0.40%		(1.40%)
EffectiveIncomeTaxRateReconciliationPenalties							(3.70%)		1.90%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent							(2.20%)		5.50%
EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsAct	[2]						(33.10%)
Other (e)							0.10%		(0.60%)	[3]	0.00%	[4]
Effective income tax rate							(3.30%)		38.30%		32.20%
Amount of Impairment to Carrying Amount of Regulatory Assets	[5]						$ 35
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate							35.00%		35.00%		35.00%
State income taxes, net of Federal income tax benefit (d)							3.00%		3.30%	[1]	1.00%
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Percent							10.00%		(7.80%)		0.80%
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Percent											(1.30%)
Effective Income Tax Rate Reconciliation, Deduction, Medicare Prescription Drug Benefit, Percent											(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference							(2.20%)		(2.30%)		(1.50%)
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent							0.00%	[6]	0.00%		0.00%
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent							(4.80%)		(8.20%)		(3.40%)
Noncontrolling interests							(0.30%)		0.30%		(0.50%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent							0.00%		(1.70%)		(2.40%)
EffectiveIncomeTaxRateReconciliationPenalties							(1.30%)		0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent							(5.70%)		(1.10%)
EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsAct	[2]						(130.10%)
Other (e)							0.40%		1.50%	[3]	0.00%	[4]
Effective income tax rate							(96.20%)		33.20%		27.10%
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate							35.00%		35.00%		35.00%
State income taxes, net of Federal income tax benefit (d)							5.70%		5.60%	[1]	4.90%
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Percent							(0.00%)		(0.00%)		(0.00%)
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Percent											0.00%
Effective Income Tax Rate Reconciliation, Deduction, Medicare Prescription Drug Benefit, Percent											(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference							(0.20%)		(0.30%)		(0.30%)
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent							0.30%	[6]	(0.60%)		(0.10%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent							0.00%		0.00%		0.00%
Noncontrolling interests							0.00%		0.00%		0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent							1.30%		0.00%		0.00%
EffectiveIncomeTaxRateReconciliationPenalties							0.00%		4.50%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent							0.00%		0.00%
EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsAct	[2]						0.10%
Other (e)							0.20%		0.10%	[3]	0.20%	[4]
Effective income tax rate							42.40%		44.30%		39.70%
Amount of Impairment to Carrying Amount of Regulatory Assets							$ 3
PECO Energy Co [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate							35.00%		35.00%		35.00%
State income taxes, net of Federal income tax benefit (d)							0.60%		1.30%	[1]	1.00%
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Percent							(0.00%)		(0.00%)		(0.00%)
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Percent											0.00%
Effective Income Tax Rate Reconciliation, Deduction, Medicare Prescription Drug Benefit, Percent											(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference							(0.10%)		(0.10%)		(0.10%)
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent							(13.80%)	[6]	(9.60%)		(8.70%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent							0.00%		0.00%		0.00%
Noncontrolling interests							0.00%		0.00%		0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent							0.00%		0.00%		0.00%
EffectiveIncomeTaxRateReconciliationPenalties							0.00%		0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent							0.00%		0.00%
EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsAct	[2]						(2.30%)
Other (e)							(0.10%)		(1.20%)	[3]	0.20%	[4]
Effective income tax rate							19.30%		25.40%		27.40%
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate							35.00%		35.00%		35.00%
State income taxes, net of Federal income tax benefit (d)							5.40%		5.00%	[1]	5.30%
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Percent							(0.00%)		(0.00%)		(0.00%)
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Percent											0.00%
Effective Income Tax Rate Reconciliation, Deduction, Medicare Prescription Drug Benefit, Percent											0.10%
Amortization of investment tax credit, including deferred taxes on basis difference							(0.10%)		(0.10%)		(0.10%)
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent							0.10%	[6]	(2.70%)		(0.70%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent							0.00%		0.00%		0.00%
Noncontrolling interests							0.00%		0.00%		0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent							0.00%		0.00%		0.00%
EffectiveIncomeTaxRateReconciliationPenalties							0.00%		0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent							0.00%		0.00%
EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsAct	[2]						0.90%
Other (e)							0.20%		0.00%	[3]	0.00%	[4]
Effective income tax rate							41.50%		37.20%		39.60%
Amount of Impairment to Carrying Amount of Regulatory Assets							$ 5
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate							35.00%		35.00%		35.00%
State income taxes, net of Federal income tax benefit (d)							3.20%		15.70%	[1]	6.70%
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Percent							(0.00%)		(0.00%)		(0.00%)
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Percent											0.00%
Effective Income Tax Rate Reconciliation, Deduction, Medicare Prescription Drug Benefit, Percent											(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference							(0.10%)	[7]	(0.20%)		(0.10%)
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent							(0.40%)	[6]	(22.80%)		(5.80%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent							0.00%		0.00%		0.00%
Noncontrolling interests							0.00%		0.00%		0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent							0.00%		0.00%		0.00%
EffectiveIncomeTaxRateReconciliationPenalties							(6.30%)		0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent							0.00%		23.50%
EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsAct	[2]						2.70%
Other (e)							(0.20%)		(1.80%)	[3]	(0.50%)	[4]
Effective income tax rate							33.90%		49.40%		35.30%
Amount of Impairment to Carrying Amount of Regulatory Assets							$ 14
Delmarva Power and Light Company [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate							35.00%		35.00%	[7]	35.00%
State income taxes, net of Federal income tax benefit (d)							5.40%		52.70%	[1],[7]	1.70%
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Percent							(0.00%)		(0.00%)	[7]	(0.00%)
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Percent											0.00%
Effective Income Tax Rate Reconciliation, Deduction, Medicare Prescription Drug Benefit, Percent											(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference							(0.20%)	[7]	(3.70%)	[7]	(0.40%)
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent							2.00%	[6]	(25.50%)	[7]	(2.30%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent							0.00%		0.00%	[7]	0.00%
Noncontrolling interests							0.00%		0.00%	[7]	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent							0.00%		0.00%	[7]	0.00%
EffectiveIncomeTaxRateReconciliationPenalties							(7.80%)		0.00%	[7]
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent							0.00%		112.90%	[7]
EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsAct	[2]						2.50%
Other (e)							0.10%		(2.20%)	[3],[7]	5.20%	[4]
Effective income tax rate							37.00%		169.20%	[7]	39.20%
Amount of Impairment to Carrying Amount of Regulatory Assets							$ 6
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate							35.00%		35.00%	[7]	35.00%
State income taxes, net of Federal income tax benefit (d)							5.60%		6.20%	[1],[7]	5.70%
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Percent							(0.00%)		(0.00%)	[7]	(0.00%)
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Percent											0.00%
Effective Income Tax Rate Reconciliation, Deduction, Medicare Prescription Drug Benefit, Percent											(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference							(0.40%)	[7]	0.80%	[7]	(0.60%)
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent							3.60%	[6]	10.30%	[7]	(1.30%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent							0.00%		0.00%	[7]	0.00%
Noncontrolling interests							0.00%		0.00%	[7]	0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent							0.00%		0.00%	[7]	0.00%
EffectiveIncomeTaxRateReconciliationPenalties							(19.80%)		0.00%	[7]
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent							0.00%		(44.90%)	[7]
EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsAct	[2]						1.60%
Other (e)							(0.40%)		1.30%	[3],[7]	6.40%	[4]
Effective income tax rate							25.20%		8.70%	[7]	45.20%
Amount of Impairment to Carrying Amount of Regulatory Assets							$ 7
Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Amount of Impairment to Carrying Amount of Regulatory Assets	[5]						$ 27
Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate				35.00%			35.00%
State income taxes, net of Federal income tax benefit (d)				5.80%	[1]		4.80%
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Percent				(0.00%)			(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference				1.40%			(0.20%)
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent				39.00%			1.10%	[6]
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent				0.00%			0.00%
Noncontrolling interests				0.00%			0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent				0.00%			0.00%
EffectiveIncomeTaxRateReconciliationPenalties				(0.70%)			(9.50%)
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent				(89.00%)			0.00%
EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsAct	[2]						6.40%
Other (e)				3.30%	[3]		(0.10%)
Effective income tax rate				(5.20%)			37.50%
Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
U.S. Federal statutory rate		35.00%									35.00%
State income taxes, net of Federal income tax benefit (d)		11.90%	[1]								6.60%
Effective Income Tax Rate Reconciliation, Tax Contingency, Other, Percent		(0.00%)									(0.00%)
Effective Income Tax Rate Reconciliation, Deduction, Qualified Production Activity, Percent											0.00%
Effective Income Tax Rate Reconciliation, Deduction, Medicare Prescription Drug Benefit, Percent											(0.00%)
Amortization of investment tax credit, including deferred taxes on basis difference		(0.90%)									(0.20%)
Effective Income Tax Rate Reconciliation,Other Reconciling Items, Percent		(13.50%)									(4.30%)
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Percent		0.00%									0.00%
Noncontrolling interests		0.00%									0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Percent		0.00%									0.00%
EffectiveIncomeTaxRateReconciliationPenalties		0.00%
Effective Income Tax Rate Reconciliation, Tax Settlement, Other, Percent		11.10%
Other (e)		3.60%	[3]								(3.20%)	[4]
Effective income tax rate		47.20%									33.90%

[1] Includes a remeasurement of uncertain state income tax positions for Pepco and DPL.

[2] Included are impacts for TJCA other than the corporate rate change, including revisions further limiting tax deductions for compensation of certain highest paid executives, the write-off of foreign tax credit carryforwards, and loss of a 2015 domestic production activities deduction due to an NOL carryback.

[3] At PECO, includes a cumulative adjustment related to an anticipated gas repairs tax return accounting method change. The method change request was filed and accepted in 2017. No change to the results recorded as of December 31, 2016

[4] Includes impacts of the PHI Global Settlement for Pepco, DPL, ACE and PHI.

[5] Exelon reflects the consolidated regulatory asset impairments of ComEd, BGE, Pepco, DPL and ACE, and PHI reflects the consolidated regulatory asset impairments of Pepco, DPL and ACE.

[6] Includes the charges related to the transmission-related income tax regulatory asset for Exelon, ComEd, BGE, PHI, Pepco, DPL, and ACE of $35 million, $3 million, $5 million, $27 million, $14 million, $6 million, and $7 million, respectively (See Footnote 3 - Regulatory Matters).

[7] DPL and ACE recognized a loss before income taxes for the year ended December 31, 2016, and PHI recognized a loss before income taxes for the period of March 24, 2016, through December 31, 2016. As a result, positive percentages represent an income tax benefit for the periods presented.