Severance - Severance Liabilities (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended	9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Restructuring Reserve [Roll Forward]
Severance Costs		$ 1	$ 8		$ 10	$ 12
Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance					88
Severance Costs	[1]				33
Payments for Restructuring					(24)
Ending Balance		97			97
Exelon Generation Co L L C [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	0	7		4	10
Exelon Generation Co L L C [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance					36
Severance Costs	[1]				25
Payments for Restructuring					(7)
Ending Balance		54			54
Commonwealth Edison Co [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	0	0		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		1	1	$ 1	4
Pepco Holdings LLC [Member] | Successor [Member] | Employee Severance [Member]
Restructuring Reserve [Roll Forward]
Beginning Balance					29
Severance Costs	[1]				3
Payments for Restructuring					(11)
Ending Balance		21			21
Potomac Electric Power Company [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	[2]	1	0		2	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]	0	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]	0	$ 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 $2 million for amounts billed by BSC through intercompany allocations for the nine months ended September 30, 2017 and $1 million and $2 million for the three and nine months ended September 30, 2016, respectively. The amounts above for ComEd include $1 million for amounts billed by BSC through intercompany allocations for the three and nine months ended September 30, 2016. The amounts above for PHI include less than $1 million and $1 million billed by BSC through intercompany allocations for the three and nine months ended September 30, 2017, respectively, and $1 million for the three and nine months ended September 30, 2016. Amounts billed by PHISCO to Pepco were $1 million and $2 million for the three and nine months ended September 30, 2017, respectively. Amounts billed by PHISCO to DPL and ACE were $1 million, each, for the nine months ended September 30, 2017. Pepco, DPL and ACE did not have any ongoing severance plans for the three and nine months ended September 30, 2016.