Discontinued Operations - Additional Information (Detail) (USD $)	3 Months Ended				3 Months Ended		9 Months Ended	12 Months Ended	3 Months Ended	9 Months Ended			3 Months Ended
	Mar. 31, 2013	Sep. 30, 2014 Pepco Energy Services [Member]	Dec. 31, 2013 Pepco Energy Services [Member]	Dec. 31, 2013 Pepco Energy Services [Member] Maximum [Member]	Jun. 30, 2013 Discontinued Operations [Member]	Mar. 31, 2013 Discontinued Operations [Member]	Sep. 30, 2014 Discontinued Operations [Member]	Dec. 31, 2012 Discontinued Operations [Member]	Mar. 31, 2013 Discontinued Operations [Member] PHI [Member]	Sep. 30, 2013 Discontinued Operations [Member] PHI [Member]	Sep. 30, 2013 Discontinued Operations [Member] PHI [Member] Proceeds From Early Termination [Member]	Sep. 30, 2013 Discontinued Operations [Member] PHI [Member] Payment Paid From Early Termination [Member]	Mar. 31, 2013 Discontinued Operations [Member] Power Delivery [Member]	Mar. 31, 2013 Discontinued Operations [Member] Other Non-Regulated [Member]	Mar. 31, 2013 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											$ 873,000,000	$ 2,000,000,000
Net pre-tax gain / loss										(3,000,000)
Loss on early termination of finance leases held in trust, after-tax										(2,000,000)
After-tax non-cash charges	377,000,000				6,000,000	323,000,000
Non-cash pre-tax charge						373,000,000
After-tax effect of revised lease rerun	313,000,000					313,000,000
After-tax non-cash charge						16,000,000			70,000,000
Interest benefit on uncertain tax positions													12,000,000
Interest expense on uncertain tax positions														16,000,000	66,000,000
Penalties associated with re-assessment of tax positions							0
Maximum percentage of penalty on the amount of additional taxes due							20.00%
Derivatives		0	0
Cash collateral posted		2,000,000	3,000,000
Letters of credit posted				1,000,000
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						(4,000,000)
Net of tax loss reclassified into Income from Discontinued operations, Net of Income Taxes						$ (2,000,000)