Severance - Severance Liabilities (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Restructuring Reserve [Roll Forward]
Severance Costs		$ 5	$ 2	$ 9	$ 4
Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance				88
Severance Costs	[1]			25
Payments for Restructuring				(18)
Ending Balance		95		95
Exelon Generation Co L L C [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	1	1	4	3
Exelon Generation Co L L C [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance				36
Severance Costs	[1]			17
Payments for Restructuring				(4)
Ending Balance		49		49
Commonwealth Edison Co [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	1	1	2	1
Commonwealth Edison Co [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance				3
Severance Costs	[1]			1
Payments for Restructuring				(1)
Ending Balance		3		3
PECO Energy Co [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance				0
Severance Costs	[1]			0
Payments for Restructuring				0
Ending Balance		0		0
Baltimore Gas and Electric Company [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance				0
Severance Costs	[1]			0
Payments for Restructuring				0
Ending Balance		0		0
Pepco Holdings LLC [Member] | Successor [Member]
Restructuring Reserve [Roll Forward]
Severance Costs		3	0	3	0
Pepco Holdings LLC [Member] | Successor [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance				29
Severance Costs	[1]			3
Payments for Restructuring				(10)
Ending Balance		22		22
Potomac Electric Power Company [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	1	0	1	0
Potomac Electric Power Company [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance				0
Severance Costs	[1]			0
Payments for Restructuring				0
Ending Balance		0		0
Delmarva Power and Light Company [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	1	0	1	0
Delmarva Power and Light Company [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance				0
Severance Costs	[1]			0
Payments for Restructuring				0
Ending Balance		0		0
Atlantic City Electric Company [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	1	$ 0	1	$ 0
Atlantic City Electric Company [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance				0
Severance Costs	[1]			0
Payments for Restructuring				0
Ending Balance		$ 0		$ 0

[1] (a)Includes salary continuance and health and welfare severance benefits.

[2] The amounts above for Generation include less than $1 million and $1 million for amounts billed by BSC through intercompany allocations for the three and six months ended June 30, 2017, respectively, and $1 million and $2 million for the three and six months ended June 30, 2016, respectively. The amounts above for ComEd include less than $1 million and $1 million for amounts billed by BSC through intercompany allocations for the three and six months ended June 30, 2017, respectively, and less than $1 million and $1 million for the three and six months ended June 30, 2016, respectively. Amounts billed by PHISCO to Pepco, DPL and ACE were $1 million, each, for both three and six months ended June 30, 2017. Pepco, DPL and ACE did not have any ongoing severance plans for the three and six months ended June 30, 2016.