Income Taxes - Narrative (Details) - USD ($) $ in Millions			3 Months Ended				9 Months Ended	12 Months Ended
		Jul. 27, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 1999
Income Taxes [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible		$ 71
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent								21.00%	35.00%	35.00%
Limitation on Deductible Interest Expense									100.00%
Allowable Expensing For Cost Of Qualified Property									30.00%
Unrecognized Tax Benefits			$ 477				$ 916	$ 477	$ 743	$ 916		$ 1,078
Unrecognized Tax Benefits, Income Tax Penalties Expense								0	(2)	106
Unrecognized Tax Benefits, Increase Resulting from Settlements with Taxing Authorities		9
Decrease in Unrecognized Tax Benefits is Reasonably Possible		90	241					241
Income taxes			26					120	(126)	753
Unrecognized Tax Benefits, Period Increase (Decrease)								(251)	(196)	(21)
Taxes accrued			412					412	373
Unrecognized Tax Benefits, Income Tax Penalties Accrued			(17)					(17)	(17)
Tax positions for which there is uncertainty about the timing of tax benefits							83		7	83
Unrecognized Tax Benefits that Would Impact Effective Tax Rate		$ 20	463				633	463	523	$ 633
Regulatory Liabilities			10,203					10,203	10,388
Regulatory Assets			9,459					9,459	$ 9,288
Like kind exchange [Member]
Income Taxes [Line Items]
Deferred gain on sale of property													$ 1,200
Unrecognized Tax Benefits, Income Tax Penalties Expense								$ 90
Decrease in Unrecognized Tax Benefits is Reasonably Possible				$ 33
Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent								21.00%	35.00%	35.00%
Unrecognized Tax Benefits			408				490	$ 408	$ 468	$ 490		534
Unrecognized Tax Benefits, Income Tax Penalties Expense								0	0	0
Decrease in Unrecognized Tax Benefits is Reasonably Possible			33					33
Income taxes								(108)	(1,376)	282
Unrecognized Tax Benefits, Period Increase (Decrease)								(36)	(17)	(20)
Taxes accrued			226					226	444
Unrecognized Tax Benefits, Income Tax Penalties Accrued			0					0	0
Tax positions for which there is uncertainty about the timing of tax benefits							7			7
Unrecognized Tax Benefits that Would Impact Effective Tax Rate			408				483	408	461	483
Allocation of federal tax benefit under tax sharing agreement			155				94	$ 155	$ 102	$ 94
Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent								21.00%	35.00%	35.00%
Unrecognized Tax Benefits			2				(12)	$ 2	$ 2	$ (12)		142
Unrecognized Tax Benefits, Income Tax Penalties Expense								0	0	86
Income taxes								168	417	301
Unrecognized Tax Benefits, Period Increase (Decrease)								0	0	0
Taxes accrued			71					71	60
Unrecognized Tax Benefits, Income Tax Penalties Accrued			0					0	0
Tax positions for which there is uncertainty about the timing of tax benefits							(12)			$ (12)
Unrecognized Tax Benefits that Would Impact Effective Tax Rate			2					2	2
Allocation of federal tax benefit under tax sharing agreement			1					1
Regulatory Liabilities			6,343					$ 6,343	6,577
Regulatory Assets									$ 1,279
Commonwealth Edison Co [Member] | Like kind exchange [Member]
Income Taxes [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible				2
PECO Energy Co [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent								21.00%	35.00%	35.00%
Unrecognized Tax Benefits			0				0	$ 0	$ 0	$ 0		0
Unrecognized Tax Benefits, Income Tax Penalties Expense								0	0	0
Income taxes								6	104	149
Unrecognized Tax Benefits, Period Increase (Decrease)								0	0	0
Taxes accrued			28					28	15
Unrecognized Tax Benefits, Income Tax Penalties Accrued			0					0	0
Allocation of federal tax benefit under tax sharing agreement			48				18	48	16	18
Regulatory Liabilities			596					$ 596	690
Regulatory Assets									410
Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible							120		$ 120	$ 120
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent								21.00%	35.00%	35.00%
Unrecognized Tax Benefits			0				120	$ 0	$ 120	$ 120		120
Unrecognized Tax Benefits, Income Tax Penalties Expense								0	0	0
Decrease in Unrecognized Tax Benefits is Reasonably Possible			120					120
Income taxes								74	218	174
Unrecognized Tax Benefits, Period Increase (Decrease)								(120)	0	0
Taxes accrued			46					46	71
Unrecognized Tax Benefits, Income Tax Penalties Accrued			0					0	0
Allocation of federal tax benefit under tax sharing agreement			26				8	26	10	8
Regulatory Liabilities			1,269					$ 1,269	1,163
Regulatory Assets									571
Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible							59		$ 59	$ 59
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent								21.00%	35.00%	35.00%
Unrecognized Tax Benefits			0				80	$ 0	$ 59	$ 80		8
Unrecognized Tax Benefits, Income Tax Penalties Expense								0	0	0
Decrease in Unrecognized Tax Benefits is Reasonably Possible			66					66
Income taxes								13	105	41
Unrecognized Tax Benefits, Period Increase (Decrease)								(66)	(21)	0
Taxes accrued			58					58	68
Unrecognized Tax Benefits, Income Tax Penalties Accrued			0					0	0
Unrecognized Tax Benefits that Would Impact Effective Tax Rate							21			21
Regulatory Liabilities			829					$ 829	832
Regulatory Assets									891
Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible							21		$ 21	$ 21
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent								21.00%	35.00%	35.00%	[1]
Unrecognized Tax Benefits			0				37	$ 0	$ 21	$ 37		3
Unrecognized Tax Benefits, Income Tax Penalties Expense								0	0	0
Decrease in Unrecognized Tax Benefits is Reasonably Possible			22					22
Income taxes								22	71	22
Unrecognized Tax Benefits, Period Increase (Decrease)								(22)	(16)	0
Taxes accrued			4					4	4
Unrecognized Tax Benefits, Income Tax Penalties Accrued			0					0	0
Unrecognized Tax Benefits that Would Impact Effective Tax Rate							16			$ 16
Regulatory Liabilities			665					$ 665	635
Regulatory Assets									314
Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible									$ 14
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent								21.00%	35.00%	35.00%	[1]
Unrecognized Tax Benefits			14				22	$ 14	$ 14	$ 22		0
Unrecognized Tax Benefits, Income Tax Penalties Expense								0	0	0
Income taxes								12	26	(4)
Unrecognized Tax Benefits, Period Increase (Decrease)								0	(22)	0
Taxes accrued			5					5	5
Unrecognized Tax Benefits, Income Tax Penalties Accrued			0					0	0
Unrecognized Tax Benefits that Would Impact Effective Tax Rate							22			22
Regulatory Liabilities			420					$ 420	422
Regulatory Assets									430
Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Increase in Unrecognized Tax Benefits is Reasonably Possible							80		$ 94	80
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent								21.00%	35.00%
Unrecognized Tax Benefits			45				$ 172	$ 45	$ 125	172
Income taxes								35	217
Unrecognized Tax Benefits, Period Increase (Decrease)								(88)	(61)
Taxes accrued			74					74	61
Unrecognized Tax Benefits, Income Tax Penalties Accrued			0					0	0
Unrecognized Tax Benefits that Would Impact Effective Tax Rate									32
Allocation of federal tax benefit under tax sharing agreement			2					2	7
Regulatory Liabilities			1,948					1,948	1,928
Regulatory Assets									3,047
Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	[1]						35.00%
Income taxes							$ 3
Unrecognized Tax Benefits that Would Impact Effective Tax Rate			31				93	31		93
Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent						35.00%
Unrecognized Tax Benefits							172			172		$ 22
Decrease in Unrecognized Tax Benefits is Reasonably Possible			88					88
Income taxes						$ 17
Unrecognized Tax Benefits, Period Increase (Decrease)										0
Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Deferred								(98)	(471)	600
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit									146
Internal Revenue Service (IRS) [Member] | Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Deferred								(347)	(2,005)	(254)
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit									19
Internal Revenue Service (IRS) [Member] | Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Deferred								145	523	379
Internal Revenue Service (IRS) [Member] | PECO Energy Co [Member]
Income Taxes [Line Items]
Deferred								10	28	72
Internal Revenue Service (IRS) [Member] | Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Deferred								47	101	88
Internal Revenue Service (IRS) [Member] | Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Deferred								(21)	114	136
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit									21
Internal Revenue Service (IRS) [Member] | Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Deferred								13	82	97
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit									16
Internal Revenue Service (IRS) [Member] | Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Deferred								18	34	22
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit									22
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Deferred								24	250
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Deferred							283
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit									59
Internal Revenue Service (IRS) [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Deferred						10
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Deferred								17	162	78
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit			425					425
Unrecognized Tax Benefits that Would Impact Effective Tax Rate			411					411
Increase (Decrease) in Deferred Income Taxes				50	$ 16
Increase (Decrease) in Income Taxes				50
State and Local Jurisdiction [Member] | Exelon Generation Co L L C [Member]
Income Taxes [Line Items]
Deferred								(83)	1	(2)
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit			411					411
Increase (Decrease) in Deferred Income Taxes				53	5
Increase (Decrease) in Income Taxes				53
State and Local Jurisdiction [Member] | Commonwealth Edison Co [Member]
Income Taxes [Line Items]
Deferred								117	136	63
State and Local Jurisdiction [Member] | PECO Energy Co [Member]
Income Taxes [Line Items]
Deferred								(16)	(9)	5
State and Local Jurisdiction [Member] | Baltimore Gas and Electric Company [Member]
Income Taxes [Line Items]
Deferred								32	49	31
State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Deferred								6	13	16
Increase (Decrease) in Deferred Income Taxes				1	16
State and Local Jurisdiction [Member] | Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Deferred								12	13	12
Increase (Decrease) in Deferred Income Taxes				2	1
State and Local Jurisdiction [Member] | Atlantic City Electric Company [Member]
Income Taxes [Line Items]
Deferred								8	4	$ 0
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit			14					14
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible			14					14
Deferred								9	$ 32
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit			14					14
Increase (Decrease) in Deferred Income Taxes				4	$ 17
Increase (Decrease) in Income Taxes				3
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] | Successor [Member]
Income Taxes [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible			$ 21					$ 21
Deferred							$ 13
State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member] | Predecessor [Member]
Income Taxes [Line Items]
Deferred						$ 7
Net Regulatory Liabilities Associated With Marginal State Income Tax Rates [Member] | State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Regulatory Liabilities				1
Net Regulatory Liabilities Associated With Marginal State Income Tax Rates [Member] | State and Local Jurisdiction [Member] | Delmarva Power & Light Company [Member]
Income Taxes [Line Items]
Regulatory Liabilities				2
Net Regulatory Liabilities Associated With Marginal State Income Tax Rates [Member] | State and Local Jurisdiction [Member] | Pepco Holdings LLC [Member]
Income Taxes [Line Items]
Regulatory Liabilities				1
Net Regulatory Assets Associated With Marginal State Income Tax Rates [Member] | State and Local Jurisdiction [Member] | Potomac Electric Power Company [Member]
Income Taxes [Line Items]
Regulatory Assets				$ 1

[1] 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.