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, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Current Tax (Benefit) Expense
Federal									$ (137)	$ (128)	$ (166)
State and local									(26)	(9)	(40)
Total Current Tax (Benefit) Expense									(163)	(137)	(206)
Deferred Tax Expense (Benefit)
Federal									261	393	254
State and local									41	65	58
Investment tax credit amortization									(1)	(2)	(3)
Total Deferred Tax Expense									301	456	309
Consolidated Income Tax Expense Related to Continuing Operations	13	34	45	46	39	65	30	185	138	319	103
Potomac Electric Power Co [Member]
Current Tax (Benefit) Expense
Federal									(79)	(39)	(84)
State and local									(3)	(1)	(27)
Total Current Tax (Benefit) Expense									(82)	(40)	(111)
Deferred Tax Expense (Benefit)
Federal									150	96	127
State and local									24	24	33
Investment tax credit amortization										(1)	(1)
Total Deferred Tax Expense									174	119	159
Consolidated Income Tax Expense Related to Continuing Operations	10	38	28	16	17	40	20	2	92	79	48
Delmarva Power & Light Co/De [Member]
Current Tax (Benefit) Expense
Federal									(45)	(8)	(9)
State and local											(1)
Total Current Tax (Benefit) Expense									(45)	(8)	(10)
Deferred Tax Expense (Benefit)
Federal									99	53	44
State and local									12	12	11
Investment tax credit amortization									(1)	(1)	(1)
Total Deferred Tax Expense									110	64	54
Consolidated Income Tax Expense Related to Continuing Operations	14	13	13	25	17	14	9	16	65	56	44
Atlantic City Electric Co [Member]
Current Tax (Benefit) Expense
Federal									(7)	(23)	(31)
State and local									(2)	(10)	(12)
Total Current Tax (Benefit) Expense									(9)	(33)	(43)
Deferred Tax Expense (Benefit)
Federal									30	28	46
State and local									7	25	16
Investment tax credit amortization										(1)	(1)
Total Deferred Tax Expense									37	52	61
Consolidated Income Tax Expense Related to Continuing Operations	$ 4	$ 14	$ 4	$ 6	$ 5	$ 13	$ 4	$ (3)	$ 28	$ 19	$ 18