Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2010
Significant Accounting Policies [Line Items]
Unbilled revenue	$ 139,000,000	$ 172,000,000
Taxes included in gross revenues	$ 322,000,000	$ 321,000,000	$ 346,000,000
Restricted stock awards vesting period	1 year	1 year
Unbilled receivables billing period	1 month
Estimated fair value of an asset	Greater than 50%
AFUDC for borrowed funds	$ 8,000,000	$ 7,000,000	7,000,000
AFUDC for equity component	$ 14,000,000	13,000,000	11,000,000
Number of subsidiaries, allocated	3
Retained earnings	$ 617,000,000	565,000,000
Asset Removal Costs [Member]
Significant Accounting Policies [Line Items]
Regulatory liabilities	$ 211,000,000	250,000,000
Maximum [Member]
Significant Accounting Policies [Line Items]
Original maturities of cash and cash equivalents	3 months
Time-Based Restricted Stock Units were Granted to Each Non-Employee Director [Member]
Significant Accounting Policies [Line Items]
Restricted stock awards vesting period	3 years
Performance Based Restricted Stock Units [Member]
Significant Accounting Policies [Line Items]
Restricted stock awards vesting period	3 years
Delmarva Power & Light Co/De [Member]
Significant Accounting Policies [Line Items]
Unbilled revenue	$ 37,000,000	63,000,000
Taxes included in gross revenues	$ 18,000,000	16,000,000	17,000,000
Unbilled receivables billing period	1 month
Estimated fair value of an asset	Greater than 50%
AFUDC for borrowed funds	$ 1,000,000	1,000,000	2,000,000
AFUDC for equity component	$ 1,000,000	2,000,000	$ 2,000,000
Preferred stock, shares outstanding	0
Retained earnings	$ 625,000,000	641,000,000
Delmarva Power & Light Co/De [Member] | Asset Removal Costs [Member]
Significant Accounting Policies [Line Items]
Regulatory liabilities	$ 153,000,000	$ 166,000,000
Delmarva Power & Light Co/De [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Original maturities of cash and cash equivalents	3 months
Delmarva Power & Light Co/De [Member] | Transmission and Distribution [Member]
Significant Accounting Policies [Line Items]
Annual Depreciation Rate	2.60%	2.60%	2.60%
Atlantic City Electric Co [Member]
Significant Accounting Policies [Line Items]
Unbilled revenue	$ 26,000,000	$ 32,000,000
Taxes included in gross revenues	$ 0	1,000,000	$ 11,000,000
Unbilled receivables billing period	1 month
Awards received from the U.S. DOE				$ 19,000,000
AFUDC for borrowed funds	$ 1,000,000	1,000,000
AFUDC for equity component	$ 1,000,000	1,000,000
Preferred stock, shares outstanding	0
Retained earnings	$ 235,000,000	$ 209,000,000
Securitization debt capitalization rate	30.00%
Atlantic City Electric Co [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Original maturities of cash and cash equivalents	3 months
AFUDC for borrowed funds			1,000,000
AFUDC for equity component			$ 1,000,000
Atlantic City Electric Co [Member] | Transmission and Distribution [Member]
Significant Accounting Policies [Line Items]
Annual Depreciation Rate	2.60%	2.60%	2.80%
Potomac Electric Power Co [Member]
Significant Accounting Policies [Line Items]
Unbilled revenue	$ 76,000,000	$ 77,000,000
Taxes included in gross revenues	$ 304,000,000	304,000,000	$ 318,000,000
Unbilled receivables billing period	1 month
Awards received from the U.S. DOE				$ 149,000,000
AFUDC for borrowed funds	$ 6,000,000	5,000,000	5,000,000
AFUDC for equity component	$ 12,000,000	10,000,000	$ 9,000,000
Preferred stock, shares outstanding	0
Retained earnings	$ 1,118,000,000	1,077,000,000
Potomac Electric Power Co [Member] | Asset Removal Costs [Member]
Significant Accounting Policies [Line Items]
Regulatory liabilities	$ 58,000,000	$ 84,000,000
Potomac Electric Power Co [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Original maturities of cash and cash equivalents	3 months
Potomac Electric Power Co [Member] | Transmission and Distribution [Member]
Significant Accounting Policies [Line Items]
Annual Depreciation Rate	2.30%	2.30%	2.20%