Supplemental Financial Information Supplemental Financial Information - Utility Taxes (Details) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
	Mar. 31, 2016	Jun. 30, 2016	Mar. 23, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		$ 217		$ 132	$ 369	$ 279
Exelon Generation Co L L C [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		27		24	55	51
Commonwealth Edison Co [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		60		55	119	117
PECO Energy Co [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		32		32	66	67
Baltimore Gas and Electric Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		21		21	45	44
Pepco Holdings LLC [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes	$ 84	77	$ 77	81		166
Potomac Electric Power Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		73		77	152	157
Delmarva Power and Light Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		4		4	9	9
Atlantic City Electric Company [Member]
Supplemental Income Statement Information [Line Items]
Utilities Operating Expense, Taxes		$ 0		$ 0	$ 0	$ 0