Severance - Ongoing Severance Plans (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 Cost and Reserve [Line Items]
Severance Costs		$ 1	$ 8		$ 10	$ 12
Exelon Generation Co L L C [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	0	7		4	10
Exelon Generation Co L L C [Member] | Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs			1		2	2
Commonwealth Edison Co [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	0	0		2	1
Commonwealth Edison Co [Member] | Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs			1			1
Pepco Holdings LLC [Member] | Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		0	1		1	1
Pepco Holdings LLC [Member] | Successor [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		1	1	$ 1	4
Potomac Electric Power Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	1	0		2	0
Potomac Electric Power Company [Member] | Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		1			2
Delmarva Power and Light Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	0	0		1	0
Delmarva Power and Light Company [Member] | Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs					1
Atlantic City Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	$ 0	$ 0		1	$ 0
Atlantic City Electric Company [Member] | Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs					$ 1

[1] 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.