Income Taxes - Provision for Consolidated Income Taxes from Continuing Operations (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current Tax (Benefit) Expense
Federal									$ (3)	$ (137)	$ (128)
State and local									12	(26)	(9)
Total Current Tax Expense (Benefit)									9	(163)	(137)
Deferred Tax Expense (Benefit)
Federal									92	261	393
State and local									30	41	65
Investment tax credit amortization									(2)	(1)	(2)
Total Deferred Tax Expense									120	301	456
Consolidated Income Tax Expense Related to Continuing Operations	$ 23	$ 49	$ 27	$ 30	$ 13	$ 34	$ 45	$ 46	129	138	319
Potomac Electric Power Co [Member]
Current Tax (Benefit) Expense
Federal									(57)	(79)	(39)
State and local									6	(3)	(1)
Total Current Tax Expense (Benefit)									(51)	(82)	(40)
Deferred Tax Expense (Benefit)
Federal									125	150	96
State and local									24	24	24
Investment tax credit amortization											(1)
Total Deferred Tax Expense									149	174	119
Consolidated Income Tax Expense Related to Continuing Operations	36	32	18	12	10	38	28	16	98	92	79
Delmarva Power & Light Co/De [Member]
Current Tax (Benefit) Expense
Federal									(26)	(45)	(8)
State and local									2
Total Current Tax Expense (Benefit)									(24)	(45)	(8)
Deferred Tax Expense (Benefit)
Federal									73	99	53
State and local									1	12	12
Investment tax credit amortization									(1)	(1)	(1)
Total Deferred Tax Expense									73	110	64
Consolidated Income Tax Expense Related to Continuing Operations	14	9	5	21	14	13	13	25	49	65	56
Atlantic City Electric Co [Member]
Current Tax (Benefit) Expense
Federal									(2)	(7)	(23)
State and local									3	(2)	(10)
Total Current Tax Expense (Benefit)									1	(9)	(33)
Deferred Tax Expense (Benefit)
Federal									25	30	28
State and local									5	7	25
Investment tax credit amortization											(1)
Total Deferred Tax Expense									30	37	52
Consolidated Income Tax Expense Related to Continuing Operations	$ 15	$ 7	$ 7	$ 2	$ 4	$ 14	$ 4	$ 6	$ 31	$ 28	$ 19