Regulatory Matters - Narrative (Details)				1 Months Ended	3 Months Ended					6 Months Ended	9 Months Ended
		Jun. 03, 2016 USD ($)	Apr. 30, 2012 MW	May 31, 2014 USD ($)	Sep. 30, 2016 USD ($)		Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2016 USD ($)	Sep. 30, 2016 USD ($)		Sep. 30, 2015 USD ($)	Aug. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)		Jul. 31, 2014 USD ($)	Aug. 31, 2010 USD ($)
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					$ 11,432,000,000						$ 11,432,000,000				$ 6,824,000,000
Business Combination, Integration Related Costs					20,000,000				$ 22,000,000		123,000,000		$ 84,000,000
Capital Expenditures Incurred but Not yet Paid											338,000,000		59,000,000
Regulatory Liabilities					4,985,000,000						4,985,000,000				4,570,000,000
Regulatory assets					10,022,000,000						10,022,000,000				6,065,000,000
Regulatory Liability, Current					548,000,000						548,000,000				369,000,000
Other Commitment					6,497,000,000			$ 508,000,000			6,497,000,000			$ 513,000,000
Fair Value, Net Asset (Liability)					2,400,000,000						2,400,000,000
Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					1,192,000,000						1,192,000,000				1,113,000,000
Business Combination, Integration Related Costs					0				3,000,000		(6,000,000)		9,000,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount											94,000,000
Capital Expenditures Incurred but Not yet Paid											42,000,000		$ 62,000,000
Regulatory Liabilities					3,781,000,000						3,781,000,000				3,614,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount											$ 90,000,000
Approved ROE											11.50%
Public Utilities, Requested Rate Increase (Decrease), Percentage											8.64%		8.59%
Regulatory assets					987,000,000						$ 987,000,000				895,000,000
Regulatory Liability, Current					204,000,000						204,000,000				155,000,000
Other Commitment					226,000,000						226,000,000
Commonwealth Edison Co [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount											138,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount											139,000,000
Public Utilities, Approved Rate Increase (Decrease), Amount											$ 1,000,000
Requested Debt and Equity Return on Distribution											6.71%		6.69%
ICC Approved Rate Increase (Decrease), Amount											$ 1,000,000
PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					1,688,000,000						1,688,000,000				1,617,000,000
Business Combination, Integration Related Costs					1,000,000				1,000,000		3,000,000		$ 4,000,000
Capital Expenditures Incurred but Not yet Paid											4,000,000		(23,000,000)
Regulatory Liabilities					679,000,000						679,000,000				639,000,000
Regulatory assets					1,651,000,000						1,651,000,000				1,583,000,000
Regulatory Liability, Current					128,000,000						128,000,000				112,000,000
Other Commitment					210,000,000						210,000,000
Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					722,000,000						722,000,000				781,000,000
Business Combination, Integration Related Costs					1,000,000				2,000,000		(3,000,000)		4,000,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount											28,000,000
Customer Refund Liability, Noncurrent					30,000,000						30,000,000
Capital Expenditures Incurred but Not yet Paid											(17,000,000)		14,000,000
Regulatory Liabilities					172,000,000						172,000,000				222,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount											12,000,000
Estimated number of smart meters to be installed																		2,000,000
Total smart grid and smart meter investment grant amount																		$ 480,000,000
Reimbursements received from the DOE																		$ 200,000,000
Regulatory assets					508,000,000						508,000,000				514,000,000
Customer Refund					30,000,000						$ 30,000,000
Rate Of Return On Common Equity In Federal Energy Regulatory Committee Complaint											10.50%
Regulatory Liability, Current					54,000,000						$ 54,000,000				38,000,000
Other Commitment					263,000,000						263,000,000
Proposed Capital Expenditure											13,000,000
Baltimore Gas and Electric Company [Member] | Gas Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount		$ 48,000,000									78,000,000
Approved ROE		9.65%
Baltimore Gas and Electric Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount											116,000,000
Public Utilities, Approved Rate Increase (Decrease), Amount		$ 44,000,000
Approved ROE		9.75%
ICC Approved Rate Increase (Decrease), Amount		$ 44,000,000
Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Business Combination, Integration Related Costs					9,000,000				10,000,000		29,000,000		30,000,000
Unregulated Operating Revenue											101,000,000
Customer Refund Liability, Noncurrent					20,000,000						20,000,000
Capital Expenditures Incurred but Not yet Paid											289,000,000		48,000,000
Customer Refund					20,000,000						20,000,000
License Costs											27,000,000
Other Commitment					5,679,000,000						5,679,000,000						$ 91,000,000
Exelon Generation Co L L C [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Purchase Obligation					3,000,000						3,000,000
Exelon Generation Co L L C [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Purchase Obligation					7,000,000						7,000,000
PEPCO Holdings Inc [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Commitment					37,000,000						37,000,000
PEPCO Holdings Inc [Member] | Predecessor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															2,582,000,000
Regulatory Liabilities															213,000,000
Regulatory assets															2,277,000,000
Regulatory Liability, Current															66,000,000
PEPCO Holdings Inc [Member] | Successor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					3,595,000,000						3,595,000,000
Regulatory Liabilities					268,000,000						268,000,000
Regulatory assets					2,945,000,000						2,945,000,000
Regulatory Liability, Current					101,000,000						101,000,000
Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					798,000,000						798,000,000				801,000,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount											(23,000,000)
Capital Expenditures Incurred but Not yet Paid											(15,000,000)		(1,000,000)
Regulatory Liabilities					44,000,000						44,000,000				44,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount											2,000,000
Approved ROE							10.60%
Regulatory assets					676,000,000						$ 676,000,000				661,000,000
Public Utilities, Requested Return on Equity, Percentage							10.60%
Power Plant Output | MW			661,000,000
Rate Of Return On Common Equity In Federal Energy Regulatory Committee Complaint											10.50%
CapitalProjectFundedByEntity				$ 500,000,000
Capital ProjectFundedByBonds				375,000,000
CapitalProjectFundedByAgency				$ 125,000,000
Regulatory Liability, Current					20,000,000						$ 20,000,000				15,000,000
Other Commitment					15,000,000						15,000,000
Current Year Revenue Adjustment											(15,000,000)
Requested ROE							10.60%
Potomac Electric Power Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount					82,000,000		$ 103,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount							127,000,000			$ 86,000,000
Potomac Electric Power Company [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Power Plant Output | MW			650,000,000
Proposed Capital Expenditure							16,000,000
Potomac Electric Power Company [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Power Plant Output | MW			700,000,000
Projected Capital Expenditures							32,000,000
Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					359,000,000						359,000,000				371,000,000
Business Combination, Integration Related Costs					2,000,000				0		18,000,000		2,000,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount											(14,000,000)
Capital Expenditures Incurred but Not yet Paid											10,000,000		2,000,000
Regulatory Liabilities					$ 146,000,000						146,000,000				160,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount											8,000,000
Requested Debt and Equity Return on Distribution					10.60%
Public Utilities, Interim Rate Increase (Decrease), Amount							$ 2,500,000
Regulatory assets					$ 297,000,000						$ 297,000,000				299,000,000
Public Utilities, Requested Return on Equity, Percentage							10.60%
Rate Of Return On Common Equity In Federal Energy Regulatory Committee Complaint											10.50%
Regulatory Liability, Current					46,000,000						$ 46,000,000				49,000,000
Other Commitment					11,000,000						11,000,000
Current Year Revenue Adjustment											(12,000,000)
Requested ROE							10.60%
Delmarva Power and Light Company [Member] | Gas Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount							$ 21,500,000
Delmarva Power and Light Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount							57,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount					66,000,000		62,800,000
Delmarva Power and Light Company [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Projected Capital Expenditures					5,000,000
Delmarva Power and Light Company [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Projected Capital Expenditures					9,000,000
Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					501,000,000						501,000,000				512,000,000
Business Combination, Integration Related Costs					2,000,000				$ 0		17,000,000		1,000,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount											(6,000,000)
Capital Expenditures Incurred but Not yet Paid											(2,000,000)		0
Regulatory Liabilities					36,000,000						36,000,000				25,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount											8,000,000
Public Utilities, Interim Rate Increase (Decrease), Amount							$ 19,000,000	$ 9,000,000
Regulatory assets					412,000,000						$ 412,000,000				414,000,000
Rate Of Return On Common Equity In Federal Energy Regulatory Committee Complaint											10.50%
Regulatory Liability, Current					35,000,000						$ 35,000,000				18,000,000
Other Commitment					9,000,000						9,000,000
Current Year Revenue Adjustment											0
Atlantic City Electric Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount					45,000,000
ICC Approved Rate Increase (Decrease), Amount					45,000,000
Under Recovered Energy And Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					74,000,000						74,000,000				84,000,000
Under Recovered Energy And Transmission Costs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[1]				31,000,000						31,000,000				43,000,000
Business Combination, Integration Related Costs													7,000,000
Under Recovered Energy And Transmission Costs [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					0						0				1,000,000	[2]
Under Recovered Energy And Transmission Costs [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[3]				25,000,000						25,000,000				40,000,000
Under Recovered Energy And Transmission Costs [Member] | PEPCO Holdings Inc [Member] | Predecessor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															33,000,000
Under Recovered Energy And Transmission Costs [Member] | PEPCO Holdings Inc [Member] | Successor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					18,000,000						18,000,000
Under Recovered Energy And Transmission Costs [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					1,000,000						1,000,000				9,000,000	[4]
Under Recovered Energy And Transmission Costs [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[5]				8,000,000						8,000,000				11,000,000
Under Recovered Energy And Transmission Costs [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[6]				9,000,000						9,000,000				13,000,000
Merger Integration Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					23,000,000						23,000,000				6,000,000
Merger Integration Costs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															0
Merger Integration Costs [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					0						0				0
Merger Integration Costs [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[7]				10,000,000						10,000,000				6,000,000
Merger Integration Costs [Member] | PEPCO Holdings Inc [Member] | Predecessor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															0
Merger Integration Costs [Member] | PEPCO Holdings Inc [Member] | Successor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					13,000,000						13,000,000
Merger Integration Costs [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					10,000,000	[8]					10,000,000	[8]			0
Merger Integration Costs [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					3,000,000	[9]					3,000,000	[9]			0
Merger Integration Costs [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					0						0				0
Under Recovered Distribution Service Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					232,000,000						232,000,000				189,000,000
Under Recovered Distribution Service Costs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[10]				232,000,000						232,000,000				189,000,000
Business Combination, Integration Related Costs											11,000,000		$ 11,000,000
Under Recovered Distribution Service Costs [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					0						0				0
Under Recovered Distribution Service Costs [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					0						0				0
Under Recovered Distribution Service Costs [Member] | PEPCO Holdings Inc [Member] | Predecessor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															0
Under Recovered Distribution Service Costs [Member] | PEPCO Holdings Inc [Member] | Successor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					0						0
Under Recovered Distribution Service Costs [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					0						0				0
Under Recovered Distribution Service Costs [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					0						0				0
Under Recovered Distribution Service Costs [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					0						0				0
AMI Expenses [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					704,000,000						704,000,000				399,000,000
AMI Expenses [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					160,000,000						160,000,000				140,000,000
AMI Expenses [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					53,000,000						53,000,000				63,000,000
AMI Expenses [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					235,000,000						235,000,000				196,000,000	[11]
Regulatory assets					235,000,000						235,000,000				196,000,000
Amount of Impairment to Carrying Amount of Regulatory Assets					52,000,000						52,000,000
AMI Expenses [Member] | Baltimore Gas and Electric Company [Member] | Gas Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount											37,000,000
AMI Expenses [Member] | Baltimore Gas and Electric Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount											104,000,000
AMI Expenses [Member] | PEPCO Holdings Inc [Member] | Predecessor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															267,000,000
AMI Expenses [Member] | PEPCO Holdings Inc [Member] | Successor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					256,000,000						256,000,000
AMI Expenses [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					171,000,000	[11]					171,000,000	[11]			180,000,000
AMI Expenses [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					85,000,000	[11]					85,000,000	[11]			87,000,000
AMI Expenses [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					0						0				0
Energy Efficiency And Demand Response Programs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					642,000,000						642,000,000				279,000,000
Energy Efficiency And Demand Response Programs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					0						0				0
Energy Efficiency And Demand Response Programs [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					1,000,000						1,000,000				1,000,000
Energy Efficiency And Demand Response Programs [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					289,000,000						289,000,000				278,000,000
Energy Efficiency And Demand Response Programs [Member] | PEPCO Holdings Inc [Member] | Predecessor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets															401,000,000
Energy Efficiency And Demand Response Programs [Member] | PEPCO Holdings Inc [Member] | Successor [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					352,000,000						352,000,000
Energy Efficiency And Demand Response Programs [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					254,000,000						254,000,000				289,000,000
Energy Efficiency And Demand Response Programs [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					98,000,000						98,000,000				111,000,000
Energy Efficiency And Demand Response Programs [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					0						0				$ 1,000,000
Legacy AMI [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					55,000,000						55,000,000
Legacy AMI [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					75,000,000						75,000,000
Legacy AMI [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					$ 14,000,000						$ 14,000,000

[1] As of September 30, 2016, ComEd’s regulatory asset of $31 million included $24 million associated with transmission costs recoverable through its FERC approved formula rate and $7 million of Constellation merger and integration costs to be recovered upon FERC approval. As of September 30, 2016, ComEd’s regulatory liability of $72 million included $43 million related to over-recovered energy costs and $29 million associated with revenues received for renewable energy requirements. As of December 31, 2015, ComEd’s regulatory asset of $43 million included $5 million related to under-recovered energy costs, $31 million associated with transmission costs recoverable through its FERC approved formula rate, and $7 million of Constellation merger and integration costs to be recovered upon FERC approval. As of December 31, 2015, ComEd’s regulatory liability of $53 million included $29 million related to over-recovered energy costs and $24 million associated with revenues received for renewable energy requirements.

[2] As of September 30, 2016, PECO's regulatory liability of $59 million included $30 million related to over-recovered costs under the DSP program, $13 million related to the over-recovered natural gas costs under the PGC, $10 million related to over-recovered non-bypassable transmission service charges and $6 million related to over-recovered electric transmission costs. As of December 31, 2015, PECO's regulatory asset of $1 million related to under-recovered non-bypassable transmission service charges. As of December 31, 2015, PECO's regulatory liability of $60 million included $35 million related to over-recovered costs under the DSP program, $22 million related to the over-recovered natural gas costs under the PGC and $3 million related to the over-recovered electric transmission costs.

[3] As of September 30, 2016, BGE's regulatory asset of $25 million included $3 million of costs associated with transmission costs recoverable through its FERC approved formula rate, $19 million related to under-recovered electric energy costs, $3 million of abandonment costs to be recovered upon FERC approval, and $1 million related to under-recovered natural gas costs. As of December 31, 2015, BGE’s regulatory asset of $40 million included $12 million of costs associated with transmission costs recoverable through its FERC approved formula rate and $28 million related to under-recovered electric energy costs. As of December 31, 2015, BGE’s regulatory liability of $18 million related to $14 million of over-recovered transmission costs and $5 million of over-recovered natural gas costs, offset by $1 million of abandonment costs to be recovered upon FERC approval.

[4] As of September 30, 2016, Pepco's regulatory liability of $17 million included $9 million of over-recovered transmission costs and $8 million of over-recovered electric energy costs. As of December 31, 2015, Pepco's regulatory asset of $9 million included $5 million of transmission costs recoverable through its FERC approved formula rate and $4 million of recoverable abandonment costs. As of December 31, 2015, Pepco's regulatory liability of $16 million included $14 million of over-recovered transmission costs and $2 million of over-recovered electric energy costs.

[5] As of September 30, 2016, DPL's regulatory asset of $8 million included $1 million of transmission costs recoverable through its FERC approved formula rate and $7 million of under-recovered electric energy costs. As of September 30, 2016, DPL's regulatory liability of $11 million included $6 million of over-recovered electric energy costs and $5 million of over-recovered transmission costs. As of December 31, 2015, DPL's regulatory asset of $11 million included $7 million of transmission costs recoverable through its FERC approved formula rate, $3 million of recoverable abandonment costs, and $1 million of under-recovered electric energy costs. As of December 31, 2015, DPL's regulatory liability of $19 million included $4 million related to the over-recovered natural gas costs under the GCR mechanism, $4 million of over-recovered electric energy costs, and $11 million of over-recovered transmission costs.

[6] As of September 30, 2016, ACE's regulatory asset of $9 million included $4 million of transmission costs recoverable through its FERC approved formula rate and $5 million of under-recovered electric energy costs. As of September 30, 2016, ACE's regulatory liability of $12 million included $7 million of over-recovered transmission costs and $5 million of over-recovered electric energy costs. As of December 31, 2015, ACE's regulatory asset of $13 million included $2 million of transmission costs recoverable through its FERC approved formula rate and $11 million of under-recovered electric energy costs. As of December 31, 2015, ACE's regulatory liability of $8 million related to over-recovered transmission costs.

[7] As of September 30, 2016, BGE's regulatory asset of $10 million included $6 million of previously incurred PHI acquisition costs as authorized by the June 2016 rate case order.

[8] epresents previously incurred PHI acquisition costs expected to be recovered in distribution rates

[9] .

[10] As of September 30, 2016, ComEd’s regulatory asset of $232 million was comprised of $178 million for the 2014 - 2016 annual reconciliations and $54 million related to significant one-time events including $24 million of deferred storm costs, $11 million of Constellation and PHI merger and integration related costs and $19 million of smart meter related costs. As of December 31, 2015, ComEd’s regulatory asset of $189 million was comprised of $142 million for the 2014 and 2015 annual reconciliations and $47 million related to significant one-time events, including $36 million of deferred storm costs and $11 million of Constellation merger and integration related costs. See Note 4— Merger, Acquisitions, and Dispositions of the Exelon 2015 Form 10-K for further information.

[11] $134 million for Pepco and $40 million for DPL, of which $75 million for Pepco and $14 million for DPL relates to retired legacy meters which are not earning a return