Severance Severance - Narrative (Details) $ in Millions		1 Months Ended		3 Months Ended				9 Months Ended
		Jun. 30, 2017 USD ($)	Aug. 31, 2015	Sep. 30, 2017 USD ($)		Sep. 30, 2016 USD ($)		Sep. 30, 2017 USD ($)		Sep. 30, 2016 USD ($)
Restructuring Cost and Reserve [Line Items]
Severance Costs				$ 1		$ 8		$ 10		$ 12
Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Number of Positions Eliminated			500
Severance Costs				7	[1]	1	[2]	6	[1]	18	[2]
Facility Closing [Member] | Three Mile Island [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		$ 17
Corporate, Non-Segment [Member] | Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Number of Positions Eliminated			250
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]
Restructuring and Related Cost, Expected Number of Positions Eliminated			250
Severance Costs				$ 7	[1]	1	[2]	6	[1]	13	[2]
Exelon Generation Co L L C [Member] | Facility Closing [Member] | Three Mile Island [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		$ 17
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

[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.