Severance Severance - Liabilities Rollforward (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Beginning Balance		$ 88	$ 35
Severance Costs		14	19
Payments		(29)	(46)
Ending Balance		94	88
Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	35	99
Exelon Generation Co L L C [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance		36	23
Severance Costs	[2]	6	13
Payments		(9)	(9)
Ending Balance		58	36
Exelon Generation Co L L C [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	31	22
Commonwealth Edison Co [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance		3	3
Severance Costs	[2]	3	3
Payments		(2)	(2)
Ending Balance		3	3
Commonwealth Edison Co [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	2	2
PECO Energy Co [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance		0	0
Severance Costs	[2]	1	1
Payments		0	0
Ending Balance		0	0
PECO Energy Co [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	0	0
Baltimore Gas and Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance		0	1
Severance Costs	[2]	0	1
Payments		0	(1)
Ending Balance		0	0
Baltimore Gas and Electric Company [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	0	0
Pepco Holdings LLC [Member] | Successor [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance		29	0
Severance Costs	[2]	4	1
Payments		(12)	(27)
Ending Balance		20	29
Pepco Holdings LLC [Member] | Successor [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	3	56
Potomac Electric Power Company [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance		0	0
Severance Costs	[2]	2	0
Payments		0	(1)
Ending Balance		0	0
Potomac Electric Power Company [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	0	1
Delmarva Power and Light Company [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance		0	0
Severance Costs	[2]	1	0
Payments		0	(1)
Ending Balance		0	0
Delmarva Power and Light Company [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	0	1
Atlantic City Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance		0	0
Severance Costs	[2]	1	0
Payments		0	0
Ending Balance		0	0
Atlantic City Electric Company [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]	$ 0	$ 0

[1] Includes salary continuance and health and welfare severance benefits.

[2] 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