Severance - Severance Benefit Related to the PHI Merger (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Severance Costs			$ 19	$ 18
Regulatory Assets		$ 11,388	11,388	6,824
PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]		57
Exelon Generation Co L L C [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[2]		13	15
Exelon Generation Co L L C [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]		9
Exelon Generation Co L L C [Member] | Corporate, Non-Segment [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs			8
Commonwealth Edison Co [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[2]		3	2
Regulatory Assets		1,167	1,167	1,113
Commonwealth Edison Co [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]		2
Commonwealth Edison Co [Member] | Corporate, Non-Segment [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs			2
PECO Energy Co [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[2]		1	0
Regulatory Assets		1,710	1,710	1,617
PECO Energy Co [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]		1
PECO Energy Co [Member] | Corporate, Non-Segment [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs			1
Baltimore Gas and Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[2]		1	1
Regulatory Assets		712	712	781
Baltimore Gas and Electric Company [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]		1
Baltimore Gas and Electric Company [Member] | Corporate, Non-Segment [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs			1
Pepco Holdings LLC [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Regulatory Assets		20	20
Pepco Holdings LLC [Member] | Successor [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[2]	1
Regulatory Assets		3,504	3,504
Pepco Holdings LLC [Member] | Successor [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]		44
Potomac Electric Power Company [Member]
Restructuring Cost and Reserve [Line Items]
Regulatory Assets		852	852	801
Potomac Electric Power Company [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1],[3]		21
Regulatory Assets		8	8
Potomac Electric Power Company [Member] | Corporate, Non-Segment [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs			20
Delmarva Power and Light Company [Member]
Restructuring Cost and Reserve [Line Items]
Regulatory Assets		348	348	371
Delmarva Power and Light Company [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1],[4]		13
Regulatory Assets		4	4
Delmarva Power and Light Company [Member] | Corporate, Non-Segment [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs			12
Atlantic City Electric Company [Member]
Restructuring Cost and Reserve [Line Items]
Regulatory Assets		501	501	$ 512
Atlantic City Electric Company [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	[1]		10
Regulatory Assets		8	8
Atlantic City Electric Company [Member] | Corporate, Non-Segment [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs			10
Severance Costs [Member] | Potomac Electric Power Company [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Regulatory Assets		11	11
Severance Costs [Member] | Delmarva Power and Light Company [Member] | PHI Merger [Member]
Restructuring Cost and Reserve [Line Items]
Regulatory Assets		$ 4	$ 4

[1] The amounts above for Generation, ComEd, PECO, BGE, Pepco, DPL and ACE include $8 million, $2 million, $1 million, $1 million, $20 million, $12 million and $10 million, respectively, for amounts billed by BSC and/or PHISCO through intercompany allocations for the year ended December 31, 2016.

[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] Pepco established a regulatory asset of $11 million as of December 31, 2016, primarily for severance benefit costs related to the PHI merger.

[4] DPL established a regulatory asset of $4 million as of December 31, 2016, primarily for severance benefit costs related to the PHI merger.