Newly Adopted Accounting Standards - Effects of the Retrospective Application of Newly Adopted Accounting Standards on Reported Balances (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other (within other assets)	$ 129	$ 121
Prepaid expenses and other	72	63
Long-term debt	4,656	4,397
Transition bonds issued by ACE Funding	124	170
Deferred income taxes, net (within current assets)	0	0
Deferred income taxes, net (within other assets)	15	17
Other (within current liabilities)	287	305
Deferred income tax liabilities, net	3,393	3,242
Potomac Electric Power Co [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other (within other assets)	42	43
Prepaid expenses and other	20	21
Long-term debt	2,301	2,096
Other (within current liabilities)	68	93
Deferred income tax liabilities, net	1,721	1,579
Delmarva Power & Light Co/De [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other (within other assets)	1	4
Prepaid expenses and other	10	12
Long-term debt	1,061	963
Other (within current liabilities)	39	41
Deferred income tax liabilities, net	941	878
Atlantic City Electric Co [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other (within other assets)	4	5
Prepaid expenses and other	1	3
Long-term debt	1,030	882
Transition bonds issued by ACE Funding	124	170
Other (within current liabilities)	21	22
Deferred income tax liabilities, net	$ 888	855
As Filed [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other (within other assets)		166
Long-term debt		4,441
Transition bonds issued by ACE Funding		171
Deferred income taxes, net (within current assets)		50
Other (within current liabilities)		314
Deferred income tax liabilities, net		3,266
As Filed [Member] | Potomac Electric Power Co [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other (within other assets)		71
Long-term debt		2,124
Deferred income taxes, net (within current assets)		14
Other (within current liabilities)		102
Deferred income tax liabilities, net		1,584
As Filed [Member] | Delmarva Power & Light Co/De [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other (within other assets)		12
Long-term debt		971
Deferred income taxes, net (within current assets)		16
Other (within current liabilities)		42
Deferred income tax liabilities, net		893
As Filed [Member] | Atlantic City Electric Co [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other (within other assets)		12
Prepaid expenses and other		13
Long-term debt		888
Transition bonds issued by ACE Funding		171
Deferred income tax liabilities, net		865
Scenario, Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other (within other assets)		(45)
Long-term debt		(44)
Transition bonds issued by ACE Funding		(1)
Deferred income taxes, net (within current assets)		(50)
Deferred income taxes, net (within other assets)		17
Other (within current liabilities)		(9)
Deferred income tax liabilities, net		(24)
Scenario, Adjustment [Member] | Potomac Electric Power Co [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other (within other assets)		(28)
Long-term debt		(28)
Deferred income taxes, net (within current assets)		(14)
Other (within current liabilities)		(9)
Deferred income tax liabilities, net		(5)
Scenario, Adjustment [Member] | Delmarva Power & Light Co/De [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other (within other assets)		(8)
Long-term debt		(8)
Deferred income taxes, net (within current assets)		(16)
Other (within current liabilities)		(1)
Deferred income tax liabilities, net		(15)
Scenario, Adjustment [Member] | Atlantic City Electric Co [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other (within other assets)		(7)
Prepaid expenses and other		(10)
Long-term debt		(6)
Transition bonds issued by ACE Funding		(1)
Deferred income tax liabilities, net		$ (10)