Discontinued Operations - Additional Information (Detail) (USD $)	3 Months Ended							12 Months Ended
	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
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Lease investments				$ 1,237,000,000					$ 1,237,000,000
Income tax charges								(1,000,000)	30,000,000	36,000,000
Inventory assets				153,000,000				148,000,000	153,000,000
Other current assets				81,000,000				53,000,000	81,000,000
Other current liabilities				272,000,000				276,000,000	272,000,000
(Loss) Income from Discontinued Operations, net of Income Taxes	8,000,000	(11,000,000)	(319,000,000)	9,000,000	25,000,000	15,000,000	18,000,000	(322,000,000)	67,000,000	35,000,000
Pepco Energy Services [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash collateral posted				25,000,000				3,000,000	25,000,000
Conectiv Energy [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
(Loss) Income from Discontinued Operations, net of Income Taxes								0	0	(3,000,000)
Other comprehensive income from discontinued operations								0	0	0
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net accounts receivable				33,000,000				0	33,000,000
Inventory assets				3,000,000				1,000,000	3,000,000
Gross derivative assets				1,000,000				0	1,000,000
Other current assets				1,000,000				0	1,000,000
Accrued liabilities				20,000,000				1,000,000	20,000,000
Gross derivative liabilities				21,000,000				0	21,000,000
Other current liabilities				1,000,000				0	1,000,000
Cash collateral pledged to counterparties with the right to reclaim				18,000,000					18,000,000
Discontinued Operations [Member] | Quoted Prices in Active Markets for Identical Instruments (Level 1) [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross derivative liabilities				11,000,000					11,000,000
Discontinued Operations [Member] | Significant Other Observable Inputs (Level 2) [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross derivative liabilities				10,000,000					10,000,000
Maximum [Member] | Pepco Energy Services [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Letters of credit posted				1,000,000				1,000,000	1,000,000
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
After-tax non-cash charges		6,000,000	323,000,000
Other non-cash charge								373,000,000		7,000,000
After-tax effect of revised lease rerun								313,000,000
Maximum percentage of penalty on the amount of additional taxes due								20.00%
Income tax charges									16,000,000	22,000,000
Federal Income tax provision									14,000,000	14,000,000
Derivatives								0
Amount of net pre-tax loss arising during the period included in Accumulated Other Comprehensive Loss									(10,000,000)
Amount of net tax loss arising during the period included in Accumulated Other Comprehensive Loss									(6,000,000)
Pre-tax loss reclassified into Income from Discontinued operations, Before Taxes									(10,000,000)
Net of tax loss reclassified into Income from Discontinued operations, Net of Income Taxes									(6,000,000)
Outstanding commodity forward contracts or derivative positions								0
Discontinued Operations [Member] | Interest Expense [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
After-tax non-cash charge								16,000,000
Discontinued Operations [Member] | PHI [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Lease investments				1,237,000,000				0	1,237,000,000
Number of investment in lease portfolio								0	6
Net pre tax gain / loss									39,000,000	39,000,000
Discontinued Operations [Member] | Pepco Energy Services [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net (losses) gains associated with disposition								1,000,000
(Loss) Income from Discontinued Operations, net of Income Taxes								5,000,000	26,000,000	2,000,000
Discontinued Operations [Member] | Payment Paid From Early Termination [Member] | PHI [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Aggregate of net cash proceeds (payments) of lease investments									520,000,000	423,000,000
Discontinued Operations [Member] | Proceeds for Corp Repayment [Member] | PHI [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Aggregate of net cash proceeds (payments) of lease investments									202,000,000	161,000,000
Discontinued Operations [Member] | PHI [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net pre tax gain / loss								3,000,000
Loss on early termination of finance leases held in trust, after tax								2,000,000
Early termination agreement of leases	Six remaining lease investments	Six remaining lease investments
After-tax non-cash charge								70,000,000
Discontinued Operations [Member] | PHI [Member] | Proceeds From Early Termination [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Aggregate of net cash proceeds (payments) of lease investments								873,000,000
Discontinued Operations [Member] | PHI [Member] | Payment Paid From Early Termination [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Aggregate of net cash proceeds (payments) of lease investments								2,000,000,000
Discontinued Operations [Member] | Power Delivery [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Interest benefit								12,000,000
Discontinued Operations [Member] | Other Non-Regulated [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Interest expense on uncertain tax positions								16,000,000
Discontinued Operations [Member] | Corporate and Other [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Interest expense on uncertain tax positions								66,000,000
Other Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net (losses) gains associated with disposition									$ 9,000,000	$ 3,000,000