Severance - Severance Liabilities (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Restructuring Reserve [Roll Forward]
Severance Costs		$ 8	$ 4
Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance		94
Severance Costs	[1]	9
Payments for Restructuring		(16)
Ending Balance		87
Exelon Generation Co L L C [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	2	3
Exelon Generation Co L L C [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance		58
Severance Costs	[1]	3
Payments for Restructuring		(5)
Ending Balance		56
Commonwealth Edison Co [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	1	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
PECO Energy Co [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	0	0
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]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	1	0
Baltimore Gas and Electric Company [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance		0
Severance Costs	[1]	1
Payments for Restructuring		0
Ending Balance		1
Pepco Holdings LLC [Member]
Restructuring Reserve [Roll Forward]
Severance Costs		4	0
Pepco Holdings LLC [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance		20
Severance Costs	[1]	2
Payments for Restructuring		(6)
Ending Balance		16
Potomac Electric Power Company [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	2	0
Potomac Electric Power Company [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance		0
Severance Costs	[1]	(1)
Payments for Restructuring		(1)
Ending Balance		0
Delmarva Power and Light Company [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	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
Atlantic City Electric Company [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	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

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

[2] The amounts above for Generation, ComEd, PECO, BGE, and PHI include immaterial amounts billed by BSC the three months ended March 31, 2018 and 2017. Pepco, DPL and ACE include immaterial amounts billed by PHISCO for the three months ended March 31, 2018 and 2017.