Schedule I - Condensed Financial Information of Parent Company - Investment in Consolidated Companies (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Total investment in consolidated companies	$ 4,636	$ 4,256
Conectiv, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Total investment in consolidated companies	2,198	1,984
Potomac Electric Power Co [Member]
Schedule of Equity Method Investments [Line Items]
Total investment in consolidated companies	2,240	2,087
Potomac Capital Investment Corporation (PCI) [Member]
Schedule of Equity Method Investments [Line Items]
Total investment in consolidated companies	40	30
Pepco Energy Services [Member]
Schedule of Equity Method Investments [Line Items]
Total investment in consolidated companies	155	153
PHI Service Company [Member]
Schedule of Equity Method Investments [Line Items]
Total investment in consolidated companies	$ 3	$ 2