Severance Severance - Narrative (Details) - USD ($) $ in Millions		1 Months Ended		12 Months Ended
		Jun. 30, 2017	Aug. 31, 2015	Dec. 31, 2017		Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Severance Costs				$ 14		$ 19
Effect on Future Earnings, Amount			$ 400	250
Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs				6		23
Facility Closing [Member] | Three Mile Island [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		$ 17
Exelon Generation Co L L C [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]			6		13
Exelon Generation Co L L C [Member] | Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs				9	[2]	18	[3]
Exelon Generation Co L L C [Member] | Corporate, Non-Segment [Member] | Cost Management Project [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs				$ (4)	[2]	$ 7	[3]

[1] The amounts above for Generation, ComEd, PECO, BGE, and PHI include immaterial amounts billed by BSC for the years ended December 31, 2017 and 2016. Pepco, DPL, and ACE include immaterial amounts billed by PHISCO for the year ended December 31, 2017. Pepco, DPL, and ACE did not have any ongoing severance plans for the year ended December 31, 2016

[2] The amounts for Generation, ComEd, PECO, and BGE include $(4) million, $(2) million, $(1) million, and $(1) million, respectively, for amounts billed by BSC through intercompany allocations for the year ended December 31, 2017.

[3] 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 year ended December 31, 2016.