Commitments and Contingencies - Environmental Matters - Additional Information (Detail) (USD $)	0 Months Ended	1 Months Ended		3 Months Ended	12 Months Ended
	Dec. 04, 2013	Jun. 30, 2012	Jan. 31, 2011 gal	Mar. 31, 2013	Dec. 31, 2013	Dec. 31, 2011	Sep. 13, 2013 gal
Commitments and Contingencies [Line Items]
EPA costs to date to clean up site					$ 6,000,000
Estimated costs remaining to remediate the site					6,000,000
Quantity of mineral oil spill			4,500
Quantity of fluid (Gallons)							11,250
Payment of imposed penalty in respect of Environmental violation	3,000				5,000,000
Tax payment made			74,000,000
Income tax penalties			1,000,000	0
Interest expense assessed relating to disallowed deductions			28,000,000
Maximum tax penalty percentage				20.00%
Federal income tax benefits				192,000,000
Percentage of disallowed tax benefits associated with leases				100.00%
Potential interest on potential tax liability related to disallowed tax benefits				50,000,000
Deposit of additional taxes and related interest				242,000,000
New tax reporting method, effect on pre-tax earnings						7,000,000
New tax reporting method, effect on after tax earnings						5,000,000
Potomac Electric Power Co [Member]
Commitments and Contingencies [Line Items]
Quantity of mineral oil spill			4,500
Civil penalty and Supplement Environmental Projects cost		1,000,000
Quantity of fluid (Gallons)							11,250
Expense incurred on Damage					1,000,000
Payment of imposed penalty in respect of Environmental violation	3,000				1,000,000
Non-cash charge (after-tax)				377,000,000
New tax reporting method, effect on pre-tax earnings						1,000,000
Potomac Electric Power Co [Member] | Minimum [Member]
Commitments and Contingencies [Line Items]
Cost of implementation of a closure plan and cap					3,000,000
Potomac Electric Power Co [Member] | Maximum [Member]
Commitments and Contingencies [Line Items]
Cost of implementation of a closure plan and cap					6,000,000
PHI [Member]
Commitments and Contingencies [Line Items]
Civil penalty and Supplement Environmental Projects cost		1,000,000
Expense incurred on Damage					1,000,000
PHI [Member] | Minimum [Member]
Commitments and Contingencies [Line Items]
Cost of implementation of a closure plan and cap					3,000,000
PHI [Member] | Maximum [Member]
Commitments and Contingencies [Line Items]
Cost of implementation of a closure plan and cap					6,000,000
Atlantic City Electric Co [Member]
Commitments and Contingencies [Line Items]
EPA costs to date to clean up site					6,000,000
Estimated costs remaining to remediate the site					6,000,000
Non-cash charge (after-tax)				$ 377,000,000