Debt - Additional Information (Detail)				12 Months Ended
	Jan. 13, 2016 USD ($)	Jul. 30, 2015 USD ($)	May. 10, 2013 USD ($)	Dec. 31, 2015 USD ($) Sublimit	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Debt Instrument [Line Items]
Debt instrument, carrying value				$ 5,001,000,000	$ 4,817,000,000
Maturities of long term debt, 2016				340,000,000
Maturities of long term debt, 2017				131,000,000
Maturities of long term debt, 2018				285,000,000
Maturities of long term debt, 2019				30,000,000
Maturities of long term debt, 2020				20,000,000
Maturities of long term debt, thereafter				4,366,000,000
On-going commercial paper				875,000,000
Short-term debt				1,063,000,000	$ 729,000,000
Variable rate demand bonds maturing 2017				26,000,000
Variable rate demand bonds maturing 2024				33,000,000
Variable rate demand bonds maturing 2028				16,000,000
Variable rate demand bonds maturing 2029				$ 30,000,000
Variable rate demand bonds weighted average interest rate				0.13%	0.19%
Amended description of Change in Control				The Consent amends the definition of "Change in Control" in the credit agreement to mean, following consummation of the Merger, an event or series of events by which Exelon no longer owns, directly or indirectly, 100% of the outstanding shares of voting stock of Pepco Holdings.
Ownership percentage of outstanding voting stock for Change in Control				100.00%
Purchase price				$ 5,000,000	$ 12,000,000
Contract payment period				15 years	9 years
Pepco Energy Services [Member]
Debt Instrument [Line Items]
Maturities of long term debt, 2016				$ 1,000,000
Maturities of long term debt, 2017				1,000,000
Maturities of long term debt, 2018				0
Maturities of long term debt, 2019				1,000,000
Maturities of long term debt, 2020				1,000,000
Maturities of long term debt, thereafter				1,000,000
Total long-term project funding (including current maturities)				5,000,000	$ 10,000,000
Purchase price						$ 7,000,000
Contract payment period						23 years
Senior Medium Term Notes One [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				885,000,000
Medium-Term Notes [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value				40,000,000	40,000,000
First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value				4,424,000,000	3,889,000,000
Transition Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value				171,000,000	215,000,000
Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value				456,000,000	806,000,000
Commercial Paper [Member]
Debt Instrument [Line Items]
Short-term debt				$ 658,000,000	624,000,000
Unsecured Syndicated Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, termination date				Aug. 01, 2018
Line of credit facility maximum borrowing capacity				$ 1,500,000,000
Parent company credit facility letter of credit, maximum				$ 500,000,000
Same day borrowings maximum percentage amount				10.00%
Swingline loan repayment period				14 days
Credit facility borrowing capacity				$ 750,000,000
Maximum amount of credit available to parent				1,250,000,000
Subsidiary borrowing limit under parent's credit facility				$ 500,000,000
Maximum number of sublimit reallocations per year | Sublimit				8
Borrowing capacity under the credit facility				$ 851,000,000	875,000,000
Utility subsidiaries combined cash and borrowing capacity				$ 576,000,000	413,000,000
Unsecured Syndicated Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Ratio of indebtedness to total capitalization				65.00%
Ratio of deferrable interest subordinated debt to total capitalization				15.00%
Unsecured Syndicated Credit Facility [Member] | Federal Funds Effective Rate [Member]
Debt Instrument [Line Items]
Debt instrument, percentage added to reference rate				0.50%
Unsecured Syndicated Credit Facility [Member] | One Month London Interbank Offered Rate [Member]
Debt Instrument [Line Items]
Debt instrument, percentage added to reference rate				1.00%
Term Loan [Member]
Debt Instrument [Line Items]
Short-term debt				$ 300,000,000
4.15% Due 2043 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				$ 200,000,000
Debt instruments maturity date				Mar. 15, 2043
Debt instrument, interest percentage				4.15%
Debt instrument, yield percentage				3.90%
Debt instrument, premium				$ 8,000,000
Debt instrument, carrying value				$ 450,000,000	250,000,000
2.70% Due 2015 [Member] | Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument, interest percentage				2.70%
Debt instrument, carrying value					250,000,000
Repayment of first mortgage bonds				$ 250,000,000
Delmarva Power & Light Co/De [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value				1,168,000,000	1,068,000,000
Repayment of first mortgage bonds				100,000,000
Maturities of long term debt, 2016				100,000,000
Maturities of long term debt, 2017				14,000,000
Maturities of long term debt, 2018				4,000,000
Maturities of long term debt, 2019				12,000,000
Maturities of long term debt, 2020				0
Maturities of long term debt, thereafter				1,038,000,000
On-going commercial paper				500,000,000
Short-term debt				210,000,000	$ 211,000,000
Variable rate demand bonds amount				105,000,000
Variable rate demand bonds maturing 2024				33,000,000
Variable rate demand bonds maturing 2028				16,000,000
Variable rate demand bonds maturing 2029				$ 30,000,000
Variable rate demand bonds weighted average interest rate				0.13%	0.19%
Amended description of Change in Control				The Consent amends the definition of "Change in Control" in the credit agreement to mean, following consummation of the Merger, an event or series of events by which Exelon no longer owns, directly or indirectly, 100% of the outstanding shares of voting stock of Pepco Holdings.
Ownership percentage of outstanding voting stock for Change in Control				100.00%
Variable rate demand bonds maturing 2017				$ 26,000,000
Delmarva Power & Light Co/De [Member] | Medium-Term Notes [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				100,000,000
Debt instrument, carrying value				40,000,000	$ 40,000,000
Delmarva Power & Light Co/De [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value				1,050,000,000	850,000,000
Variable rate demand bonds amount				72,000,000
Delmarva Power & Light Co/De [Member] | Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value					100,000,000
Delmarva Power & Light Co/De [Member] | Commercial Paper [Member]
Debt Instrument [Line Items]
Short-term debt				$ 105,000,000	$ 106,000,000
Commercial paper weighted average interest rate				0.47%	0.26%
Weighted average maturity, in days				4 days	5 days
Delmarva Power & Light Co/De [Member] | Unsecured Syndicated Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, termination date				Aug. 01, 2018
Line of credit facility maximum borrowing capacity				$ 1,500,000,000
Parent company credit facility letter of credit, maximum				$ 500,000,000
Same day borrowings maximum percentage amount				10.00%
Swingline loan repayment period				14 days
Credit facility borrowing capacity				$ 250,000,000
Maximum amount of credit available to parent				1,250,000,000
Subsidiary borrowing limit under parent's credit facility				$ 500,000,000
Maximum number of sublimit reallocations per year | Sublimit				8
Utility subsidiaries combined cash and borrowing capacity				$ 576,000,000	$ 413,000,000
Delmarva Power & Light Co/De [Member] | Unsecured Syndicated Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Ratio of indebtedness to total capitalization				65.00%
Ratio of deferrable interest subordinated debt to total capitalization				15.00%
Delmarva Power & Light Co/De [Member] | Unsecured Syndicated Credit Facility [Member] | Federal Funds Effective Rate [Member]
Debt Instrument [Line Items]
Debt instrument, percentage added to reference rate				0.50%
Delmarva Power & Light Co/De [Member] | Unsecured Syndicated Credit Facility [Member] | One Month London Interbank Offered Rate [Member]
Debt Instrument [Line Items]
Debt instrument, percentage added to reference rate				1.00%
Delmarva Power & Light Co/De [Member] | 4.15% Due 2045 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				$ 200,000,000
Debt instruments maturity date				May 15, 2045
Debt instrument, interest percentage				4.15%
Debt instrument, carrying value				$ 200,000,000
Delmarva Power & Light Co/De [Member] | 5.00% Due 2015 [Member] | Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instruments maturity date				Jun. 01, 2015
Debt instrument, interest percentage				5.00%
Debt instrument, carrying value				$ 0	100,000,000
Atlantic City Electric Co [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value				1,039,000,000	904,000,000
Maturities of long term debt, 2016				2,000,000
Maturities of long term debt, 2017				0
Maturities of long term debt, 2018				250,000,000
Maturities of long term debt, 2019				0
Maturities of long term debt, 2020				0
Maturities of long term debt, thereafter				787,000,000
On-going commercial paper				350,000,000
Short-term debt				$ 5,000,000	127,000,000
Variable rate demand bonds amount					$ 18,000,000
Variable rate demand bonds weighted average interest rate					0.05%
Amended description of Change in Control				The Consent amends the definition of "Change in Control" in the credit agreement to mean, following consummation of the Merger, an event or series of events by which Exelon no longer owns, directly or indirectly, 100% of the outstanding shares of voting stock of Pepco Holdings.
Ownership percentage of outstanding voting stock for Change in Control				100.00%
Atlantic City Electric Co [Member] | Senior Medium Term Notes One [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				$ 227,000,000
Atlantic City Electric Co [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value				1,039,000,000	$ 904,000,000
Atlantic City Electric Co [Member] | Tax-Exempt Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				62,000,000
Atlantic City Electric Co [Member] | Transition Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value				171,000,000	215,000,000
Maturities of long term debt, 2016				46,000,000
Maturities of long term debt, 2017				35,000,000
Maturities of long term debt, 2018				31,000,000
Maturities of long term debt, 2019				18,000,000
Maturities of long term debt, 2020				20,000,000
Maturities of long term debt, thereafter				21,000,000
Atlantic City Electric Co [Member] | Commercial Paper [Member]
Debt Instrument [Line Items]
Short-term debt				$ 5,000,000	$ 127,000,000
Commercial paper weighted average interest rate				0.46%	0.27%
Weighted average maturity, in days				6 days	5 days
Atlantic City Electric Co [Member] | Unsecured Syndicated Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, termination date				Aug. 01, 2018
Line of credit facility maximum borrowing capacity				$ 1,500,000,000
Parent company credit facility letter of credit, maximum				$ 500,000,000
Same day borrowings maximum percentage amount				10.00%
Swingline loan repayment period				14 days
Credit facility borrowing capacity				$ 250,000,000
Maximum amount of credit available to parent				1,250,000,000
Subsidiary borrowing limit under parent's credit facility				$ 500,000,000
Maximum number of sublimit reallocations per year | Sublimit				8
Utility subsidiaries combined cash and borrowing capacity				$ 576,000,000	$ 413,000,000
Atlantic City Electric Co [Member] | Unsecured Syndicated Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Ratio of indebtedness to total capitalization				65.00%
Ratio of deferrable interest subordinated debt to total capitalization				15.00%
Atlantic City Electric Co [Member] | Unsecured Syndicated Credit Facility [Member] | Federal Funds Effective Rate [Member]
Debt Instrument [Line Items]
Debt instrument, percentage added to reference rate				0.50%
Atlantic City Electric Co [Member] | Unsecured Syndicated Credit Facility [Member] | One Month London Interbank Offered Rate [Member]
Debt Instrument [Line Items]
Debt instrument, percentage added to reference rate				1.00%
Atlantic City Electric Co [Member] | Term Loan [Member]
Debt Instrument [Line Items]
Debt instrument, face amount			$ 100,000,000
Debt instrument, percentage added to reference rate			0.75%
Atlantic City Electric Co [Member] | 3.50% Due 2025 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				$ 150,000,000
Debt instruments maturity date				Dec. 01, 2025
Debt instrument, interest percentage				3.50%
Debt instrument, carrying value				$ 150,000,000
Atlantic City Electric Co [Member] | 7.68% Due 2015 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt instruments maturity date				Aug. 24, 2015
Debt instrument, interest percentage				7.68%
Repayment of medium term notes				$ 15,000,000
Atlantic City Electric Co [Member] | Medium Term Notes Series C [Member]
Debt Instrument [Line Items]
Debt instruments maturity date				Aug. 24, 2015
Debt instrument, interest percentage				7.68%
Repayment of secured medium-term notes				$ 15,000,000
Potomac Electric Power Co [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value				2,335,000,000	2,135,000,000
Maturities of long term debt, 2016				0
Maturities of long term debt, 2017				0
Maturities of long term debt, 2018				0
Maturities of long term debt, 2019				0
Maturities of long term debt, 2020				0
Maturities of long term debt, thereafter				2,335,000,000
On-going commercial paper				500,000,000
Short-term debt				$ 64,000,000	104,000,000
Amended description of Change in Control				The Consent amends the definition of "Change in Control" in the credit agreement to mean, following consummation of the Merger, an event or series of events by which Exelon no longer owns, directly or indirectly, 100% of the outstanding shares of voting stock of Pepco Holdings.
Ownership percentage of outstanding voting stock for Change in Control				100.00%
Purchase price				$ 5,000,000	$ 12,000,000
Contract payment period				15 years	9 years
Potomac Electric Power Co [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				$ 885,000,000
Potomac Electric Power Co [Member] | Tax-Exempt Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				110,000,000
Potomac Electric Power Co [Member] | Commercial Paper [Member]
Debt Instrument [Line Items]
Short-term debt				$ 64,000,000	$ 104,000,000
Commercial paper weighted average interest rate				0.44%	0.28%
Weighted average maturity, in days				4 days	6 days
Potomac Electric Power Co [Member] | Unsecured Syndicated Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, termination date				Aug. 01, 2018
Line of credit facility maximum borrowing capacity				$ 1,500,000,000
Parent company credit facility letter of credit, maximum				$ 500,000,000
Same day borrowings maximum percentage amount				10.00%
Swingline loan repayment period				14 days
Credit facility borrowing capacity				$ 250,000,000
Maximum amount of credit available to parent				1,250,000,000
Subsidiary borrowing limit under parent's credit facility				$ 500,000,000
Maximum number of sublimit reallocations per year | Sublimit				8
Utility subsidiaries combined cash and borrowing capacity				$ 576,000,000	$ 413,000,000
Potomac Electric Power Co [Member] | Unsecured Syndicated Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Ratio of indebtedness to total capitalization				65.00%
Ratio of deferrable interest subordinated debt to total capitalization				15.00%
Potomac Electric Power Co [Member] | Unsecured Syndicated Credit Facility [Member] | Federal Funds Effective Rate [Member]
Debt Instrument [Line Items]
Debt instrument, percentage added to reference rate				0.50%
Potomac Electric Power Co [Member] | Unsecured Syndicated Credit Facility [Member] | One Month London Interbank Offered Rate [Member]
Debt Instrument [Line Items]
Debt instrument, percentage added to reference rate				1.00%
Potomac Electric Power Co [Member] | 4.15% Due 2043 [Member] | First Mortgage Bonds [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				$ 200,000,000
Debt instruments maturity date				Mar. 15, 2043
Debt instrument, interest percentage				4.15%
Debt instrument, yield percentage				3.90%
Debt instrument, premium				$ 8,000,000
Debt instrument, carrying value				450,000,000	250,000,000
PHI [Member] | Commercial Paper [Member]
Debt Instrument [Line Items]
Short-term debt				$ 484,000,000	$ 287,000,000
Commercial paper weighted average interest rate				0.80%	0.57%
Weighted average maturity, in days				10 days	6 days
PHI [Member] | Term Loan [Member] | Term Loan One [Member]
Debt Instrument [Line Items]
Debt instruments maturity date				Jul. 28, 2016
Debt instrument, carrying value		$ 300,000,000
Debt instrument, percentage added to reference rate		0.95%
PHI [Member] | Term Loan [Member] | $500 Million Term Loan [Member]
Debt Instrument [Line Items]
Debt instruments maturity date				Jul. 13, 2016
PHI [Member] | Term Loan [Member] | Subsequent Event [Member] | $500 Million Term Loan [Member]
Debt Instrument [Line Items]
Debt instrument, carrying value	$ 500,000,000
Debt instrument, percentage added to reference rate	0.90%