Stock-Based Compensation, Dividend Restrictions, and Calculations of Earnings Per Share of Common Stock - Common Stock Reserved and Unissued (Detail)	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares	26,569,117
DRP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares	6,104,591
Pepco Holdings Long-Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares	7,450,404
Pepco Holdings 2012 Long-Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares	7,971,832
Pepco Holdings Non-Management Directors Compensation Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares	457,211
Pepco Holdings Retirement Savings Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares	4,585,079