Severance - Severance Liabilities (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Restructuring Reserve [Roll Forward]
Severance Costs		$ 4	$ 2
Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance		88
Severance Costs	[1]	3
Payments for Restructuring		(10)
Ending Balance		81
Exelon Generation Co L L C [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	3	2
Exelon Generation Co L L C [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance		36
Severance Costs	[1]	1
Payments for Restructuring		(3)
Ending Balance		34
Commonwealth Edison Co [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	1	$ 0
Commonwealth Edison Co [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance		3
Severance Costs	[1]	0
Payments for Restructuring		0
Ending Balance		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
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
Pepco Holdings LLC [Member] | Successor [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance		29
Severance Costs	[1]	0
Payments for Restructuring		(5)
Ending Balance		24
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
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
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

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

[2] he amounts above for Generation include $1 million for amounts billed by BSC through intercompany allocations for both the three months ended March 31, 2017 and 2016. Amounts billed by BSC to ComEd were immaterial.