Stock-Based Compensation, Dividend Restrictions, and Calculations of Earnings Per Share of Common Stock - Common Stock Reserved and Unissued (Detail)	Dec. 31, 2015 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares	22,123,913
DRP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares	4,584,077
Pepco Holdings Long-Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares	6,946,614
Pepco Holdings 2012 Long-Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares	7,136,961
Pepco Holdings Retirement Savings Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares	3,456,261