Significant Accounting Policies Expected Right of Use Assets and Lease Obligations (Details)	12 Months Ended
	Dec. 31, 2018
Estimated Right of Use Assets and Lease Liabilities from Operating Leases [Line Items]
Estimated Operating Lease, Right-of-Use Asset	$1,400-$1,500
Estimated Operating Lease, Lease Liability	$1,600-$1,700
Exelon Generation Co L L C [Member]
Estimated Right of Use Assets and Lease Liabilities from Operating Leases [Line Items]
Estimated Operating Lease, Right-of-Use Asset	$1,000-$1,100
Estimated Operating Lease, Lease Liability	$1,200-$1,300
Commonwealth Edison Co [Member]
Estimated Right of Use Assets and Lease Liabilities from Operating Leases [Line Items]
Estimated Operating Lease, Right-of-Use Asset	$5-$10
Estimated Operating Lease, Lease Liability	$5-$10
PECO Energy Co [Member]
Estimated Right of Use Assets and Lease Liabilities from Operating Leases [Line Items]
Estimated Operating Lease, Right-of-Use Asset	$1-$5
Estimated Operating Lease, Lease Liability	$1-$5
Baltimore Gas and Electric Company [Member]
Estimated Right of Use Assets and Lease Liabilities from Operating Leases [Line Items]
Estimated Operating Lease, Right-of-Use Asset	$100-$120
Estimated Operating Lease, Lease Liability	$100-$120
Pepco Holdings LLC [Member]
Estimated Right of Use Assets and Lease Liabilities from Operating Leases [Line Items]
Estimated Operating Lease, Right-of-Use Asset	$250-$270
Estimated Operating Lease, Lease Liability	$300-$320
Potomac Electric Power Company [Member]
Estimated Right of Use Assets and Lease Liabilities from Operating Leases [Line Items]
Estimated Operating Lease, Right-of-Use Asset	$60-$65
Estimated Operating Lease, Lease Liability	$60-$65
Delmarva Power & Light Company [Member]
Estimated Right of Use Assets and Lease Liabilities from Operating Leases [Line Items]
Estimated Operating Lease, Right-of-Use Asset	$70-$75
Estimated Operating Lease, Lease Liability	$75-$80
Atlantic City Electric Company [Member]
Estimated Right of Use Assets and Lease Liabilities from Operating Leases [Line Items]
Estimated Operating Lease, Right-of-Use Asset	$20-$25
Estimated Operating Lease, Lease Liability	$20-$25