Regulatory Matters Regulatory Matters - Schedule of TCJA Savings (Details) - USD ($) $ in Millions													3 Months Ended
	Sep. 07, 2018	Aug. 29, 2018	Jul. 01, 2018	Jun. 27, 2018	Apr. 20, 2018	Mar. 29, 2018	Mar. 02, 2018	Feb. 09, 2018	Feb. 06, 2018	Feb. 05, 2018	Jan. 31, 2018	Jan. 18, 2018	Sep. 30, 2018
Commonwealth Edison Co [Member]
Regulatory Matters Schedule of TCJA Savings [Line Items]
Tax Savings From Tax Cuts and Jobs Act												$ 201
PECO Energy Co [Member]
Regulatory Matters Schedule of TCJA Savings [Line Items]
Tax Savings From Tax Cuts and Jobs Act						$ 71
Atlantic City Electric Company [Member]
Regulatory Matters Schedule of TCJA Savings [Line Items]
Tax Savings From Tax Cuts and Jobs Act							$ 23
Gas Distribution [Member] | PECO Energy Co [Member]
Regulatory Matters Schedule of TCJA Savings [Line Items]
Tax Savings From Tax Cuts and Jobs Act			$ 4
Gas Distribution [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Schedule of TCJA Savings [Line Items]
Tax Savings From Tax Cuts and Jobs Act											$ 31
Public Utilities, Rate Credit											2
Gas Distribution [Member] | Delmarva Power & Light Company [Member]
Regulatory Matters Schedule of TCJA Savings [Line Items]
Tax Savings From Tax Cuts and Jobs Act								$ 7
Public Utilities, Rate Credit	$ 1
Electric Distribution [Member] | PECO Energy Co [Member]
Regulatory Matters Schedule of TCJA Savings [Line Items]
Public Utilities, Rate Credit											67
Electric Distribution [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Schedule of TCJA Savings [Line Items]
Tax Savings From Tax Cuts and Jobs Act											$ 72
Electric Distribution [Member] | Delmarva Power & Light Company [Member]
Regulatory Matters Schedule of TCJA Savings [Line Items]
Tax Savings From Tax Cuts and Jobs Act								$ 19
Public Utilities, Rate Credit				$ 3
Electric Distribution [Member] | Potomac Electric Power Company [Member]
Regulatory Matters Schedule of TCJA Savings [Line Items]
Tax Savings From Tax Cuts and Jobs Act									$ 39
Public Utilities, Rate Credit	$ 20				$ 10
Electric Distribution [Member] | Atlantic City Electric Company [Member]
Regulatory Matters Schedule of TCJA Savings [Line Items]
Public Utilities, Rate Credit		$ 6
Maryland Service Territory [Member] | Electric Distribution [Member] | Delmarva Power & Light Company [Member]
Regulatory Matters Schedule of TCJA Savings [Line Items]
Tax Savings From Tax Cuts and Jobs Act										$ 31			$ 14
Public Utilities, Rate Credit													$ 2