Income Taxes - Provision for Consolidated Income Taxes from Continuing Operations (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Current Tax (Benefit) Expense
Federal									$ (128)	$ (166)	$ (72)
State and local									(9)	(40)	12
Total Current Tax (Benefit) Expense									(137)	(206)	(60)
Deferred Tax Expense (Benefit)
Federal									393	254	163
State and local									65	58	15
Investment tax credit amortization									(2)	(3)	(4)
Total Deferred Tax Expense									456	309	174
Consolidated Income Tax Expense	39	65	30	185	11	57	26	9	319	103	114
Potomac Electric Power Co [Member]
Current Tax (Benefit) Expense
Federal									(39)	(84)	(19)
State and local									(1)	(27)	(16)
Total Current Tax (Benefit) Expense									(40)	(111)	(35)
Deferred Tax Expense (Benefit)
Federal									96	127	54
State and local									24	33	19
Investment tax credit amortization									(1)	(1)	(2)
Total Deferred Tax Expense									119	159	71
Consolidated Income Tax Expense	17	40	20	2	10	35	8		79	48	36
Delmarva Power & Light Co/De [Member]
Current Tax (Benefit) Expense
Federal									(8)	(9)	(22)
State and local										(1)	8
Total Current Tax (Benefit) Expense									(8)	(10)	(14)
Deferred Tax Expense (Benefit)
Federal									53	44	53
State and local									12	11	4
Investment tax credit amortization									(1)	(1)	(1)
Total Deferred Tax Expense									64	54	56
Consolidated Income Tax Expense	17	14	9	16	10	11	9	14	56	44	42
Atlantic City Electric Co [Member]
Current Tax (Benefit) Expense
Federal									(23)	(31)	(9)
State and local									(10)	(12)	1
Total Current Tax (Benefit) Expense									(33)	(43)	(8)
Deferred Tax Expense (Benefit)
Federal									28	46	35
State and local									25	16	7
Investment tax credit amortization									(1)	(1)	(1)
Total Deferred Tax Expense									52	61	41
Consolidated Income Tax Expense	$ 5	$ 13	$ 4	$ (3)	$ 13	$ (3)	$ 9	$ (1)	$ 19	$ 18	$ 33