Discontinued Operations - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended						3 Months Ended		12 Months Ended	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2013 Corporate and Other [Member]	Mar. 31, 2014 Pepco Energy Services [Member]	Dec. 31, 2013 Pepco Energy Services [Member]	Mar. 31, 2014 Pepco Energy Services [Member] Maximum [Member]	Dec. 31, 2013 Pepco Energy Services [Member] Maximum [Member]	Mar. 31, 2014 Discontinued Operations [Member]	Mar. 31, 2013 Discontinued Operations [Member]	Dec. 31, 2012 Discontinued Operations [Member]	Mar. 31, 2014 Discontinued Operations [Member] Interest Expense [Member]	Mar. 31, 2014 Discontinued Operations [Member] PHI [Member]	Mar. 31, 2014 Discontinued Operations [Member] PHI [Member] Proceeds From Early Termination [Member]	Mar. 31, 2014 Discontinued Operations [Member] PHI [Member] Payment Paid From Early Termination [Member]	Mar. 31, 2014 Discontinued Operations [Member] Power Delivery [Member]	Mar. 31, 2014 Discontinued Operations [Member] Other Non-Regulated [Member]	Mar. 31, 2014 Discontinued Operations [Member] Corporate and Other [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	$ 2,000
Net pre tax gain / loss											3
Loss on early termination of finance leases held in trust, after tax											2
After-tax non-cash charges	377							323
Other non-cash charge							373
After-tax effect of revised lease rerun							307
After-tax non-cash charge										16	70
Interest benefit														12
Interest expense on uncertain tax positions		66													16	66
Maximum percentage of penalty on the amount of additional taxes due							20.00%
Derivatives			0	0
Cash collateral posted			2	3
Letters of credit posted					1	1
Amount of net pre-tax loss arising during the period included in Accumulated Other Comprehensive Loss									(10)
Amount of net tax loss arising during the period included in Accumulated Other Comprehensive Loss									(6)
Pre-tax loss reclassified into Income from Discontinued operations, Before Taxes									(4)
Net of tax loss reclassified into Income from Discontinued operations, Net of Income Taxes									$ (2)