Supplemental Financial Information Supplemental Financial Information - Utility Taxes (Details) - USD ($) $ in Millions		3 Months Ended
	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016	Mar. 23, 2016
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		$ 224	$ 153
Exelon Generation Co L L C [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		32	28
Commonwealth Edison Co [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		59	59
PECO Energy Co [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		31	35
Baltimore Gas and Electric Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		26	24
Pepco Holdings LLC [Member] | Predecessor [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes				$ 77
Pepco Holdings LLC [Member] | Successor [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes	$ 7	76
Potomac Electric Power Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		71	79
Delmarva Power and Light Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		5	5
Atlantic City Electric Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		$ 0	$ 0