Derivative Financial Instruments - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Ineffective portion recognized in income	$ 15,000	$ 14,000	$ 17,000
Cash collateral held	(8,000)
Letters of credit held	19,000
Interest Rate Fair Value Hedge Asset at Fair Value	5,000
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Credit exposure under off system sales	4,000
Incremental collateral for loss of investment grade credit rating	66,000
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Letters of credit posted	293,000	284,000
Cash collateral held	(35,000)	(24,000)
Letters of credit held	33,000	28,000
Cash collateral posted	497,000	347,000
Incremental collateral for loss of investment grade credit rating	1,800,000	1,900,000
Interest Rate Fair Value Hedge Asset at Fair Value	2,000
Derivative, Collateral, Obligation to Return Cash	$ 4,000	$ 8,000
Commonwealth Edison Company [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties	10
Commonwealth Edison Company [Member] | Other Contract [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties	19
Commonwealth Edison Company [Member] | Renewable Energy Program [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties	2
Commonwealth Edison Co [Member]
Derivative [Line Items]
Term of contract	20 years
Credit exposure under off system sales	$ 1,000
Incremental collateral for loss of investment grade credit rating	$ 14,000
PECO Energy Co [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged	20.00%
Incremental collateral for loss of investment grade credit rating	$ 34,000
Delmarva Power and Light Company [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating	11,000
Delmarva Power and Light Company [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Brokered Natural Gas Margin Revenue	$ 2,750
Minimum [Member] | Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged	10.00%
Minimum [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected generation hedged in next twelve months	85.00%
Expected generation hedged in year two	55.00%
Expected generation hedged in year three	26.00%
Maximum [Member] | Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged	20.00%
Maximum [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected generation hedged in next twelve months	88.00%
Expected generation hedged in year two	58.00%
Expected generation hedged in year three	29.00%
Atlantic City Electric Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	$ 6,000
PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Due From Affiliate Current Electric Gas Utility	22,000
Baltimore Gas And Electric Company Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Due From Affiliate Current Electric Gas Utility	24,000
Potomac Electric Power Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	36,000
Delmarva Power and Light Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	12,000
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	$ 28,000