Regulatory Matters - Narrative (Details) GWh in Millions			1 Months Ended	3 Months Ended									6 Months Ended	12 Months Ended
		Dec. 31, 2030	May 31, 2014 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($) GWh		Dec. 31, 2016 USD ($)		Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)		Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2017	Dec. 31, 2016 USD ($)		Jun. 01, 2019	Jun. 01, 2018	Jun. 01, 2017	Sep. 30, 2016 USD ($)	Aug. 31, 2010 USD ($)
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					$ 11,381,000,000		$ 11,388,000,000								$ 11,388,000,000
Business Combination, Integration Related Costs	[1],[2]				9,000,000					$ 102,000,000
Capital Expenditures Incurred but Not yet Paid					(298,000,000)					(290,000,000)
Regulatory Liabilities					4,939,000,000		4,789,000,000								4,789,000,000
Regulatory assets					10,051,000,000		10,046,000,000								10,046,000,000
Regulatory Liability, Current					637,000,000		602,000,000								602,000,000
Other Commitment					3,212,000,000
Fair Value, Net Asset (Liability)					2,400,000,000
Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					1,215,000,000		1,167,000,000								1,167,000,000
Business Combination, Integration Related Costs	[2]				0					(8,000,000)	[3]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount					11,000,000
Capital Expenditures Incurred but Not yet Paid					25,000,000					25,000,000
Regulatory Liabilities					3,803,000,000		3,698,000,000								3,698,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount					$ 44,000,000
Public Utilities, Interim Rate Increase (Decrease), Amount															$ (8,000,000)
Approved ROE					11.50%
Public Utilities, Requested Rate Increase (Decrease), Percentage					8.40%										8.34%
Regulatory assets					$ 1,032,000,000		977,000,000								$ 977,000,000
Regulatory Liability, Current					311,000,000		329,000,000								329,000,000
Other Commitment					219,000,000
SocialCarbonCost					16.50
NuclearFacilityPurchaseAmount					0.16
LowIncomeEnergyAssistanceContributionAnnual					$ 10,000,000
LowIncomeEnergyAssistanceContributionLength					5
Low Income Sector Consumption Reduction Targets Act 129 Phase II					0.10%
Renewable Energy Resources Cumulatively Increase					1.50%
DecouplingImpactOnOperatingRevenuesAndRegulatoryAssets					$ 16,000,000
Commonwealth Edison Co [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount					96,000,000		(18,000,000)								127,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount					78,000,000										134,000,000
Public Utilities, Approved Rate Increase (Decrease), Amount					$ 18,000,000										$ 7,000,000
Requested Debt and Equity Return on Distribution					6.47%										6.45%
ICC Approved Rate Increase (Decrease), Amount					$ 18,000,000										$ 7,000,000
Commonwealth Edison Co [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
FutureEnergyEfficiencySpending					$ 250,000,000
Renewable Energy Resources Cumulatively Increase					11.50%
Commonwealth Edison Co [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
ResidentialCustomerRateIncrease					25.00%
CommercialAndIndustrialCustomerRateIncrease					1.30%
Renewable Energy Resources Cumulatively Increase					25.00%
Commonwealth Edison Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
CumulativeAnnualEnergyEfficiencyGoal | GWh					88
PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					$ 1,748,000,000		1,710,000,000								1,710,000,000
Business Combination, Integration Related Costs	[2]				1,000,000					2,000,000
Capital Expenditures Incurred but Not yet Paid					0					(65,000,000)
Regulatory Liabilities					691,000,000		644,000,000								644,000,000
Regulatory assets					1,708,000,000		1,681,000,000								1,681,000,000
Regulatory Liability, Current					161,000,000		127,000,000								127,000,000
Other Commitment					208,000,000
Total Projected Natural Gas LTIIP Spend					762,000,000							$ 534,000,000
Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					690,000,000		712,000,000								712,000,000
Business Combination, Integration Related Costs	[2]				2,000,000					2,000,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount					26,000,000
Capital Expenditures Incurred but Not yet Paid					41,000,000					(4,000,000)
Regulatory Liabilities					161,000,000		160,000,000								160,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount					31,000,000
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					$ 499,000,000		504,000,000								504,000,000
Rate Of Return On Common Equity In Federal Energy Regulatory Committee Complaint					10.50%
Regulatory Liability, Current					$ 67,000,000		50,000,000								50,000,000
Other Commitment					266,000,000
Proposed Capital Expenditure					8,000,000
Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Business Combination, Integration Related Costs	[2]				9,000,000					16,000,000
Unregulated Operating Revenue					101,000,000
Customer Refund Liability, Noncurrent					20,000,000
Capital Expenditures Incurred but Not yet Paid					(354,000,000)					(234,000,000)
Customer Refund					20,000,000
License Costs					29,000,000
Other Commitment					2,404,000,000
Exelon Generation Co L L C [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Purchase Obligation					3,000,000
Exelon Generation Co L L C [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Purchase Obligation					7,000,000
PEPCO Holdings Inc [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Commitment					36,000,000
Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					852,000,000		852,000,000								852,000,000
Capital Expenditures Incurred but Not yet Paid					(6,000,000)					9,000,000
Regulatory Liabilities					29,000,000		31,000,000								31,000,000
Regulatory assets					$ 679,000,000		690,000,000								690,000,000
Rate Of Return On Common Equity In Federal Energy Regulatory Committee Complaint					10.50%
CapitalProjectFundedByEntity			$ 500,000,000		$ 250,000,000
Capital ProjectFundedByBonds			375,000,000		188,000,000
CapitalProjectFundedByAgency			125,000,000		62,000,000
Regulatory Liability, Current					10,000,000		11,000,000								11,000,000
Other Commitment					15,000,000
Projected Capital Expenditures			$ 1,000,000,000		500,000,000
Potomac Electric Power Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount					77,000,000		82,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount					69,000,000								$ 86,000,000
TaxAdjustmentIncludedInPublicUtilitiesRequestedRateIncreaseDecreaseAmount					$ 18,000,000
Public Utilities, Requested Rate Increase (Decrease), Percentage					10.10%				10.60%
Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					$ 367,000,000		348,000,000								348,000,000
Business Combination, Integration Related Costs	[2]				(7,000,000)	[4]				16,000,000
Capital Expenditures Incurred but Not yet Paid					9,000,000					8,000,000
Regulatory Liabilities					142,000,000		140,000,000								140,000,000
Public Utilities, Interim Rate Increase (Decrease), Amount									$ 2,500,000
Regulatory assets					$ 301,000,000		289,000,000								289,000,000
Public Utilities, Requested Return on Equity, Percentage					9.70%				10.60%
Regulatory Liability, Current					$ 47,000,000		43,000,000								43,000,000
Other Commitment					$ 11,000,000
Requested ROE					9.70%				10.60%
Delmarva Power and Light Company [Member] | Gas Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount							10,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount									$ 22,000,000
Gas Revenues Increase Settlement																				$ 0.14
Delmarva Power and Light Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount					$ 31,500,000		30,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount					60,000,000				63,000,000
Public Utilities, Approved Rate Increase (Decrease), Amount					$ 38,000,000
Approved ROE					9.60%
ICC Approved Rate Increase (Decrease), Amount					$ 38,000,000
Delmarva Power and Light Company [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Projected Capital Expenditures					4,600,000
Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					501,000,000		501,000,000								501,000,000
Business Combination, Integration Related Costs	[2]				1,000,000					13,000,000
Capital Expenditures Incurred but Not yet Paid					0					$ (9,000,000)
Regulatory Liabilities					25,000,000		25,000,000								25,000,000
Regulatory assets					407,000,000		405,000,000								405,000,000
Regulatory Liability, Current					25,000,000		25,000,000								25,000,000
Other Commitment					8,000,000
Proposed Capital Expenditure					29,000,000
Atlantic City Electric Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount					$ 70,000,000
Public Utilities, Requested Rate Increase (Decrease), Percentage					10.10%
Advanced Metering Infrastructure Costs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					$ 26,000,000		23,000,000								23,000,000
Advanced Metering Infrastructure Costs [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					140,000,000
Under Recovered Energy And Transmission Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					71,000,000		89,000,000								89,000,000
Under Recovered Energy And Transmission Costs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[5]				18,000,000		23,000,000								23,000,000
Business Combination, Integration Related Costs					8,000,000		8,000,000
Under Recovered Energy And Transmission Costs [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					0		0								0
Under Recovered Energy And Transmission Costs [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[6]				19,000,000		38,000,000								38,000,000
Under Recovered Energy And Transmission Costs [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					6,000,000		6,000,000								6,000,000
Under Recovered Energy And Transmission Costs [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[7]				5,000,000		5,000,000								5,000,000
Under Recovered Energy And Transmission Costs [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[8]				23,000,000		17,000,000								17,000,000
Merger Integration Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					32,000,000		25,000,000								25,000,000
Merger Integration Costs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets							0								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	[9]				8,000,000		10,000,000		6,000,000				6,000,000		10,000,000
Merger Integration Costs [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					11,000,000	[10]	11,000,000								11,000,000
Merger Integration Costs [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[10]				13,000,000		4,000,000								4,000,000
Merger Integration Costs [Member] | Delmarva Power and Light Company [Member] | Electric Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					8,000,000
Other Income					5,000,000
Merger Integration Costs [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					0		0								0
MergerIntegrationCostsToBeRecoveredInDelawareServiceTerritory [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[10]				8,000,000
MergerIntegrationCostsToBeRecoveredInMarylandServiceTerritory [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[10]				5,000,000
Under Recovered Distribution Service Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					211,000,000		188,000,000								188,000,000
Under Recovered Distribution Service Costs [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets	[11]				211,000,000		188,000,000								188,000,000
Business Combination, Integration Related Costs					10,000,000										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] | 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					689,000,000		701,000,000								701,000,000
AMI Expenses [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					165,000,000		164,000,000								164,000,000
AMI Expenses [Member] | PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					46,000,000		49,000,000								49,000,000
AMI Expenses [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					225,000,000		230,000,000	[12]							230,000,000	[12]
Regulatory assets					225,000,000		230,000,000								230,000,000
Amount of Impairment to Carrying Amount of Regulatory Assets					52,000,000
AMI Expenses [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					170,000,000	[12]	174,000,000								174,000,000
AMI Expenses [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					83,000,000	[12]	84,000,000								84,000,000
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					596,000,000		621,000,000								621,000,000
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					269,000,000		285,000,000								285,000,000
Energy Efficiency And Demand Response Programs [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					241,000,000		250,000,000								250,000,000
Energy Efficiency And Demand Response Programs [Member] | Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					84,000,000		85,000,000								85,000,000
Energy Efficiency And Demand Response Programs [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					1,000,000		$ 0								$ 0
Legacy AMI [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory Assets					$ 53,000,000				$ 56,000,000				$ 56,000,000
Subsequent Event [Member] | Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
EnergyEfficiencyAnnualCumulativeSavings		21.50%												6.60%
RenewableEnergyRetailLoad																	100.00%	75.00%	50.00%
Subsequent Event [Member] | Delmarva Power and Light Company [Member] | Gas Distribution [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount				$ 4,900,000
Public Utilities, Requested Return on Equity, Percentage				9.70%
Requested ROE				9.70%
Subsequent Event [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Proposed Capital Expenditure				$ 32,000,000

[1] Reflects costs (benefits) recorded at Exelon related to financing, including mark-to-market activity on forward-starting interest rate swaps.

[2] The costs incurred are classified primarily within Operating and maintenance expense in the Registrants’ respective Consolidated Statements of Operations and Comprehensive Income, with the exception of the financing costs, which are included within Interest expense. Costs do not include merger commitments discussed above.

[3] For the three months ended March 31, 2016, includes the reversal of previously incurred acquisition, integration and financing costs of $9 million, incurred at ComEd that have been deferred and recorded as a regulatory asset for anticipated recovery. See Note 5—Regulatory Matters for more information.

[4] For the three months ended March 31, 2017, includes the reversal of previously incurred acquisition, integration and financing costs of $8 million, incurred at DPL that have been deferred and recorded as a regulatory asset for anticipated recovery. See Note 5—Regulatory Matters for more information.

[5] As of March 31, 2017, ComEd’s regulatory asset of $18 million included $10 million associated with transmission costs recoverable through its FERC approved formula rate and $8 million of Constellation merger and integration costs to be recovered upon FERC approval. As of March 31, 2017, ComEd’s regulatory liability of $38 million included $6 million related to over-recovered energy costs and $32 million associated with revenues received for renewable energy requirements. As of December 31, 2016, ComEd’s regulatory asset of $23 million included $15 million associated with transmission costs recoverable through its FERC approved formula rate and $8 million of Constellation merger and integration costs to be recovered upon FERC approval. As of December 31, 2016, ComEd’s regulatory liability of $60 million included $30 million related to over-recovered energy costs and $30 million associated with revenues received for renewable energy requirements.

[6] As of March 31, 2017, PECO's regulatory liability of $66 million included $41 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 $2 million related to over-recovered electric transmission costs. As of December 31, 2016, PECO's regulatory liability of $56 million included $34 million related to over-recovered costs under the DSP program, $10 million related to over-recovered non-bypassable transmission service charges, $8 million related to the over-recovered natural gas costs under the PGC and $4 million related to the over-recovered electric transmission costs.

[7] As of March 31, 2017, Pepco's regulatory asset of $6 million included $2 million of transmission costs recoverable through its FERC approved formula rate and $4 million of under-recovered electric energy costs. As of March 31, 2017, Pepco's regulatory liability of $7 million included $2 million of over-recovered transmission costs and $5 million of over-recovered electric energy costs. As of December 31, 2016, Pepco's regulatory asset of $6 million related to under-recovered electric energy costs. As of December 31, 2016, Pepco's regulatory liability of $8 million included $5 million of over-recovered transmission costs and $3 million of over-recovered electric energy costs.

[8] As of March 31, 2017, DPL's regulatory asset of $5 million related to under-recovered electric energy costs. As of March 31, 2017, DPL's regulatory liability of $12 million included $9 million of over-recovered electric energy costs, $1 million of over-recovered transmission costs, and $2 million of over-recovered gas cost. As of December 31, 2016, DPL's regulatory asset of $5 million included $1 million of transmission costs recoverable through its FERC approved formula rate and $4 million of under-recovered electric energy costs. As of December 31, 2016, DPL's regulatory liability of $5 million included $2 million of over-recovered electric energy costs and $3 million of over-recovered transmission costs.

[9] As of March 31, 2017, ACE's regulatory asset of $23 million included $10 million of transmission costs recoverable through its FERC approved formula rate and $13 million of under-recovered electric energy costs. As of March 31, 2017, ACE's regulatory liability of $8 million included $2 million of over-recovered transmission costs and $6 million of over-recovered electric energy costs. As of December 31, 2016, ACE's regulatory asset of $17 million included $6 million of transmission costs recoverable through its FERC approved formula rate and $11 million of under-recovered electric energy costs. As of December 31, 2016, ACE's regulatory liability of $5 million included $4 million of over-recovered transmission costs and $1 million of over-recovered electric energy costs.

[10] As of March 31, 2017, BGE's regulatory asset of $8 million included $6 million of previously incurred PHI acquisition costs as authorized by the June 2016 rate case order.

[11] As of March 31, 2017, ComEd’s regulatory asset of $211 million was comprised of $158 million for the 2015 - 2017 annual reconciliations and $53 million related to significant one-time events including $17 million of deferred storm costs, $10 million of Constellation and PHI merger and integration related costs and $26 million of smart meter related costs. As of December 31, 2016, ComEd’s regulatory asset of $188 million was comprised of $134 million for the 2015 and 2016 annual reconciliations and $54 million related to significant one-time events, including $20 million of deferred storm costs and $11 million of Constellation and PHI merger and integration related costs, and $23 million of smart meter related costs. ComEd's 2015 annual reconciliation regulatory asset included a reduction of $8 million related to a ComEd-proposed refund to customers for the impact of changing its OSHA recordable rate for 2014 and 2015. See Note 4— Merger, Acquisitions, and Dispositions of the Exelon 2016 Form 10-K for further information.

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