Severance Severance - Cost Management Program-Related (Details) - USD ($) $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2017		Sep. 30, 2016		Sep. 30, 2017		Sep. 30, 2016
Restructuring Cost and Reserve [Line Items]
Severance Costs		$ 1		$ 8		$ 10		$ 12
Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		7	[1]	1	[2]	6	[1]	18	[2]
Exelon Generation Co L L C [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[3]	0		7		4		10
Exelon Generation Co L L C [Member] | Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		7	[1]	1	[2]	6	[1]	13	[2]
Exelon Generation Co L L C [Member] | Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs				1		2		2
Exelon Generation Co L L C [Member] | Corporate, Non-Segment [Member] | Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs								7
Commonwealth Edison Co [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[3]	0		0		2		1
Commonwealth Edison Co [Member] | Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		0	[1]	0	[2]	0	[1]	3	[2]
Commonwealth Edison Co [Member] | Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs				1				1
Commonwealth Edison Co [Member] | Corporate, Non-Segment [Member] | Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs								3
PECO Energy Co [Member] | Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		0	[1]	0	[2]	0	[1]	1	[2]
PECO Energy Co [Member] | Corporate, Non-Segment [Member] | Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs								1
Baltimore Gas and Electric Company [Member] | Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		$ 0	[1]	$ 0	[2]	$ 0	[1]	1	[2]
Baltimore Gas and Electric Company [Member] | Corporate, Non-Segment [Member] | Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs								$ 1

[1] Amounts billed by BSC through intercompany allocations for the nine months ended September 30, 2017 were immaterial.

[2] The amounts above for Generation, ComEd, PECO and BGE include $7 million, $3 million, $1 million and $1 million, respectively, for amounts billed by BSC through intercompany allocations for the nine months ended September 30, 2016.

[3] 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.