Goodwill (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Goodwill [Line Items]
Goodwill Beginning Balance, Gross Amount	$ 1,425	$ 1,425
Goodwill Ending Balance, Gross Amount	1,425	1,425
Accumulated Impairment Losses, Beginning Balance	18	18
Accumulated Impairment Losses, Ending Balance	18	18
Goodwill Beginning Balance, Carrying Amount	1,407	1,407
Goodwill Ending Balance, Carrying Amount	1,407	1,407
Impairment losses, Gross Amount
Accumulated Impairment Losses
Impairment losses, Carrying Amount
Delmarva Power & Light Co/De [Member]
Goodwill [Line Items]
Goodwill Beginning Balance, Gross Amount	8	8
Goodwill Ending Balance, Gross Amount	8	8
Accumulated Impairment Losses, Beginning Balance
Accumulated Impairment Losses, Ending Balance
Goodwill Beginning Balance, Carrying Amount	8	8
Goodwill Ending Balance, Carrying Amount	8	8
Impairment losses, Gross Amount
Accumulated Impairment Losses
Impairment losses, Carrying Amount