Income Taxes (Schedule Of Income Tax Expense (Benefit)) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended										12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012		Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011		Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Current Tax (Benefit) Expense
Federal											$ (76)	$ 9	$ (270)
State and local											(39)	4	(50)
Total Current Tax (Benefit) Expense											(115)	13	(320)
Deferred Tax Expense (Benefit)
Federal											216	121	300
State and local											58	19	34
Investment tax credit amortization											(3)	(4)	(3)
Total Deferred Tax Expense											271	136	331
Consolidated Income Tax Expense	14	93	[1]	35	14	6	55	54	[2]	34	156	149	11
Potomac Electric Power Co [Member]
Current Tax (Benefit) Expense
Federal											(84)	(19)	(28)
State and local											(27)	(16)	(7)
Total Current Tax (Benefit) Expense											(111)	(35)	(35)
Deferred Tax Expense (Benefit)
Federal											127	54	52
State and local											33	19	22
Investment tax credit amortization											(1)	(2)	(2)
Total Deferred Tax Expense											159	71	72
Consolidated Income Tax Expense											48	36	37
Delmarva Power & Light Co/De [Member]
Current Tax (Benefit) Expense
Federal											(9)	(22)	(37)
State and local											(1)	8	(5)
Total Current Tax (Benefit) Expense											(10)	(14)	(42)
Deferred Tax Expense (Benefit)
Federal											44	53	61
State and local											11	4	13
Investment tax credit amortization											(1)	(1)	(1)
Total Deferred Tax Expense											54	56	73
Consolidated Income Tax Expense											44	42	31
Atlantic City Electric Co [Member]
Current Tax (Benefit) Expense
Federal											(31)	(9)	(5)
State and local											(12)	1
Total Current Tax (Benefit) Expense											(43)	(8)	(5)
Deferred Tax Expense (Benefit)
Federal											46	35	33
State and local											16	7	16
Investment tax credit amortization											(1)	(1)	(1)
Total Deferred Tax Expense											61	41	48
Consolidated Income Tax Expense											$ 18	$ 33	$ 43

[1] Includes a $16 million charge related to the recognition of the tax consequences associated with the early termination of cross-border energy leases.

[2] Includes tax benefits of $14 million in the second quarter primarily associated with an interest benefit related to federal tax liabilities and a $22 million charge related to the recognition of the tax consequences associated with the early termination of cross-border energy leases.