Severance - Severance Liabilities Rollforward (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
		Mar. 23, 2016	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Beginning Balance		$ 35		$ 35	$ 50
Severance Costs				19	18
Payments				(46)	(31)
Ending Balance			$ 88	88	35
Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]			99	16
Exelon Generation Co L L C [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance		23		23	34
Severance Costs	[2]			13	15
Payments				(9)	(21)
Ending Balance			36	36	23
Exelon Generation Co L L C [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]			22	10
Commonwealth Edison Co [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance		3		3	2
Severance Costs	[2]			3	2
Payments				(2)	(1)
Ending Balance			3	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	0
Severance Costs	[2]			1	0
Payments				0	0
Ending Balance			0	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		1		1	2
Severance Costs	[2]			1	1
Payments				(1)	(1)
Ending Balance			0	0	1
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	[3]	0		0	0
Severance Costs	[2]		1
Payments	[3]			(27)	0
Ending Balance	[3]		29	29	0
Pepco Holdings LLC [Member] | Successor [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1],[3]			56	0
Pepco Holdings LLC [Member] | Predecessor [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance	[3]	0		0	3
Severance Costs	[2]	0			0
Payments	[3]				(3)
Ending Balance	[3]				0
Pepco Holdings LLC [Member] | Predecessor [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1],[3]				0
Potomac Electric Power Company [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance		0		0	1
Payments				(1)	(1)
Ending Balance			0	0	0
Potomac Electric Power Company [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]			1	0
Delmarva Power and Light Company [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance		0		0	0
Payments				(1)	0
Ending Balance			0	0	0
Delmarva Power and Light Company [Member] | Severance [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]			1	0
Atlantic City Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Beginning Balance		$ 0		0	0
Payments				0	0
Ending Balance			$ 0	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. Amounts primarily represent benefits provided for the PHI post-merger integration and the cost management program.

[2] The amounts above for Generation, ComEd, PECO, BGE and PHI include immaterial amounts billed by BSC for the years ended December 31, 2016 and 2015.

[3] For PHI, the successor period includes activity for the period from March 24, 2016 through December 31, 2016. The PHI predecessor periods include activity for the year ended December 31, 2015 and the period January 1, 2016 through March 23, 2016. There was no activity in the 2016 PHI predecessor period.