Regulatory Matters - Narrative (Details)					1 Months Ended				3 Months Ended				12 Months Ended
	Mar. 31, 2016 USD ($)	Dec. 08, 2014	Feb. 27, 2013	Apr. 30, 2012 MW	Aug. 31, 2015 USD ($)	Aug. 31, 2014 USD ($)	May. 31, 2014 USD ($)	Mar. 31, 2013 USD ($)	Mar. 31, 2016 USD ($)	Mar. 23, 2016 USD ($)	Dec. 31, 2015 USD ($)	Mar. 31, 2015	Dec. 31, 2015 USD ($)	Jul. 31, 2014 USD ($)	Aug. 31, 2010 USD ($)
Regulatory Matters Additional Narrative Information [Line Items]
Capital Expenditures Incurred but Not yet Paid									$ (290,000,000)
Regulatory Liabilities	$ 4,890,000,000								4,890,000,000		$ 4,570,000,000		$ 4,570,000,000
Regulatory assets	10,407,000,000								$ 10,407,000,000		6,065,000,000		6,065,000,000
Transmission Rate Formula, First Basis Points Credited									0.50%
Regulatory Liability, Current	512,000,000								$ 512,000,000		369,000,000		369,000,000
Other Commitment	$ 6,282,000,000								$ 6,282,000,000
Rate of Return on Common Equity, Incentive Basis Points	0.50%								0.50%
Fair Value, Net Asset (Liability)	$ 2,500,000,000								$ 2,500,000,000
Commonwealth Edison Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Capital Expenditures Incurred but Not yet Paid									25,000,000
Regulatory Liabilities	$ 3,639,000,000								3,639,000,000		$ 3,614,000,000		$ 3,614,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount									$ 138,000,000
Requested Debt and Equity Return on Distribution									6.71%			6.69%
Weighted Average Debt And Equity Return	8.47%								8.47%		8.61%		8.61%
Gross transmission revenue requirement									$ 90,000,000
Transmission revenue true up									4,000,000
Net transmission revenue requirement									$ 94,000,000
Public Utilities, Requested Rate Increase (Decrease), Percentage									8.64%			8.59%
Regulatory assets	$ 925,000,000								$ 925,000,000		$ 895,000,000		$ 895,000,000
Rate Of Return On Common Equity									11.50%
Regulatory Liability, Current	150,000,000								$ 150,000,000		155,000,000		155,000,000
Other Commitment	226,000,000								226,000,000
Prior Year Revenue Adjustment													1,000,000
Current Year Revenue Adjustment									139,000,000
PECO Energy Co [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Capital Expenditures Incurred but Not yet Paid									(65,000,000)
Regulatory Liabilities	655,000,000								655,000,000		639,000,000		639,000,000
Regulatory assets	1,605,000,000								1,605,000,000		1,583,000,000		1,583,000,000
Regulatory Liability, Current	134,000,000								134,000,000		112,000,000		112,000,000
Other Commitment	209,000,000								209,000,000
Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Customer Refund Liability, Noncurrent											13,700,000		13,700,000
Capital Expenditures Incurred but Not yet Paid									(4,000,000)
Regulatory Liabilities	$ 212,000,000								$ 212,000,000		222,000,000		$ 222,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount											$ 197,000,000
Requested ROE			8.70%
Weighted Average Debt And Equity Return	8.09%								8.09%		8.46%		8.46%
Proposed Capital Expenditure									$ 13,000,000
Gross transmission revenue requirement									12,000,000
Transmission revenue true up									3,000,000
Net transmission revenue requirement									15,000,000
Estimated number of smart meters to be installed															2,000,000
Total smart grid and smart meter investment grant amount															$ 480,000,000
Reimbursements received from the DOE															$ 200,000,000
Regulatory assets	$ 499,000,000								$ 499,000,000		$ 514,000,000		$ 514,000,000
Customer Refund											13,700,000		13,700,000
Rate Of Return On Common Equity									10.50%
Rate Of Return On Common Equity In Federal Energy Regulatory Committee Complaint			10.80%
Regulatory Liability, Current	61,000,000								$ 61,000,000		38,000,000		38,000,000
Other Commitment	262,000,000								262,000,000
Projected Investment In Smartmeters											141,000,000		141,000,000
Exelon Generation Co L L C [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Unregulated Operating Revenue									101,000,000
Customer Refund Liability, Noncurrent	20,000,000								20,000,000
Capital Expenditures Incurred but Not yet Paid									(234,000,000)
Customer Refund	20,000,000								20,000,000
License Costs									25,000,000
Other Commitment	5,468,000,000								5,468,000,000					$ 91,000,000
Exelon Generation Co L L C [Member] | Reserve for Environmental Costs [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Other Commitment	3,500,000								3,500,000
Exelon Generation Co L L C [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Minimum Purchase Obligation	3,000,000								3,000,000
Exelon Generation Co L L C [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Maximum Purchase Obligation	7,000,000								7,000,000
PEPCO Holdings Inc [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Capital Expenditures Incurred but Not yet Paid	(7,000,000)									$ 11,000,000
Rate Of Return On Common Equity In Federal Energy Regulatory Committee Complaint		11.30%
Other Commitment	37,000,000								37,000,000
Potomac Electric Power Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Customer Refund Liability, Noncurrent											14,200,000		14,200,000
Capital Expenditures Incurred but Not yet Paid									9,000,000
Regulatory Liabilities	55,000,000								$ 55,000,000		44,000,000		44,000,000
Requested Debt and Equity Return on Distribution									10.60%
Requested increase in electric revenues	127,000,000								$ 127,000,000
Proposed Capital Expenditure									16,000,000
Regulatory assets	663,000,000								663,000,000		661,000,000		661,000,000
Customer Refund											14,200,000		14,200,000
Power Plant Output | MW				661,000,000
CapitalProjectFundedByEntity							$ 500,000,000
Capital ProjectFundedByBonds							375,000,000
CapitalProjectFundedByAgency							125
Regulatory Liability, Current	26,000,000								26,000,000		15,000,000		15,000,000
Other Commitment	15,000,000								15,000,000
Projected Capital Expenditures							$ 1,000,000,000		32,000,000
Potomac Electric Power Company [Member] | Minimum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Power Plant Output | MW				650,000,000
Potomac Electric Power Company [Member] | Maximum [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Power Plant Output | MW				700,000,000
Delmarva Power and Light Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Customer Refund Liability, Noncurrent											11,900,000		11,900,000
Capital Expenditures Incurred but Not yet Paid									8,000,000
Regulatory Liabilities	166,000,000								166,000,000		160,000,000		160,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount								$ 42,000,000
Public Utilities, Approved Rate Increase (Decrease), Amount						$ 15,000,000
Approved ROE						9.70%
ICC Approved Rate Increase (Decrease), Amount						$ 15,000,000
Regulatory assets	295,000,000								295,000,000		299,000,000		299,000,000
Customer Refund											11,900,000		11,900,000
Regulatory Liability, Current	57,000,000								57,000,000		49,000,000		49,000,000
Other Commitment	12,000,000								12,000,000
Prior Year Revenue Adjustment					$ 0.26
Atlantic City Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Customer Refund Liability, Noncurrent											9,500,000		9,500,000
Capital Expenditures Incurred but Not yet Paid									(9,000,000)
Regulatory Liabilities	27,000,000								27,000,000		25,000,000		25,000,000
Public Utilities, Requested Rate Increase (Decrease), Amount									19
Public Utilities, Interim Rate Increase (Decrease), Amount									9
Requested increase in electric revenues	0								$ 0
Requested Rate Of Return Common Equity Electric Distribution									0.106
Regulatory assets	419,000,000								$ 419,000,000		414,000,000		414,000,000
Customer Refund											9,500,000		9,500,000
Regulatory Liability, Current	22,000,000								22,000,000		18,000,000		18,000,000
Other Commitment	8,000,000								8,000,000
Adjustment To Electric Revenues Increase Requested									176
AMI Expenses [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Regulatory assets	$ 212,000,000								$ 212,000,000		$ 196,000,000		$ 196,000,000
FERC Transmission Complaint [Member] | Baltimore Gas and Electric Company [Member]
Regulatory Matters Additional Narrative Information [Line Items]
Approved ROE									10.00%