Severance Severance - Liabilities Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	$ 77	$ 94	$ 88
Payments for Restructuring		(29)
Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	35	35
Payments for Restructuring	(52)
Exelon Generation Co L L C [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	47	58	36
Payments for Restructuring		(9)
Exelon Generation Co L L C [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	9	31
Payments for Restructuring	(20)
Commonwealth Edison Co [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	2	3	3
Payments for Restructuring		(2)
Commonwealth Edison Co [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	1	2
Payments for Restructuring	(2)
PECO Energy Co [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	0	0	0
Payments for Restructuring		0
PECO Energy Co [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	0	0
Payments for Restructuring	0
Baltimore Gas and Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	1	0	0
Payments for Restructuring		0
Baltimore Gas and Electric Company [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	1	0
Payments for Restructuring	0
Pepco Holdings LLC [Member] | Successor [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	7	20	29
Payments for Restructuring		(12)
Pepco Holdings LLC [Member] | Successor [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	5	3
Payments for Restructuring	(18)
Potomac Electric Power Company [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	0	0	0
Payments for Restructuring		0
Potomac Electric Power Company [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	1	0
Payments for Restructuring	(1)
Delmarva Power & Light Company [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	0	0	0
Payments for Restructuring		0
Delmarva Power & Light Company [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	0	0
Payments for Restructuring	0
Atlantic City Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	0	0	$ 0
Payments for Restructuring		0
Atlantic City Electric Company [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	0	$ 0
Payments for Restructuring	$ 0