Derivative Financial Instruments - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Derivative [Line Items]
Ineffective portion recognized in income	$ 9,000		$ 15,000		$ 14,000
Cash collateral held	(17,000)
Letters of credit held	35,000
Derivative, Fair Value, Net	1,000		6,000
InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	3,000		5,000
Commodity Contract [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	299,000		667,000
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Credit exposure under off system sales	3,000
Incremental collateral for loss of investment grade credit rating	69,000
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Letters of credit posted	367,000		293,000
Cash collateral held	(47,000)		(35,000)
Letters of credit held	44,000		33,000
Cash collateral posted	418,000		497,000
Incremental collateral for loss of investment grade credit rating	2,100,000		1,800,000
Interest Rate Fair Value Hedge Asset at Fair Value	7,000
Derivative, Collateral, Obligation to Return Cash	2,000		4,000
Exelon Generation Co L L C [Member] | InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	7,000		2,000
Exelon Generation Co L L C [Member] | InterestRateAndForeignExchangeContract [Member] | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Derivative, Fair Value, Net			1,000
Exelon Generation Co L L C [Member] | Commodity Contract [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	$ 548,000	[1]	$ 923,000	[2]
Commonwealth Edison Company [Member] | Energy Related Derivative [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties	38000000
Commonwealth Edison Company [Member] | Other Contract [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties	19000000
Commonwealth Edison Company [Member] | Renewable Energy Program [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties	31000000
Commonwealth Edison Co [Member]
Derivative [Line Items]
Term of contract	20 years
Incremental collateral for loss of investment grade credit rating	$ 7,000
PECO Energy Co [Member]
Derivative [Line Items]
Estimated Percent Of Gas Purchases Being Hedged	20.00%
Incremental collateral for loss of investment grade credit rating	$ 39,000
Delmarva Power & Light Company [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating	11,000
Delmarva Power & 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 Percent Of Gas Purchases Being Hedged	10.00%
Minimum [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected generation hedged in next twelve months	89.00%
Expected generation hedged in year two	56.00%
Expected generation hedged in year three	32.00%
Maximum [Member] | Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Estimated Percent Of Gas Purchases Being Hedged	20.00%
Maximum [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected generation hedged in next twelve months	92.00%
Expected generation hedged in year two	59.00%
Expected generation hedged in year three	35.00%
Atlantic City Electric Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Due From Affiliate Current Electric Utility	$ 5,000
PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Due From Affiliate Current Electric Gas Utility	30,000
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]
Due From Affiliate Current Electric Utility	28,000
Delmarva Power & Light Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Due From Affiliate Current Electric Utility	7,000
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Due From Affiliate Current Electric Utility	43,000
Derivative, Collateral, Obligation to Return Cash	$ 12,000

[1] Current and noncurrent assets are shown net of collateral of $121 million and $51 million, respectively, and current and noncurrent liabilities are shown net of collateral of $125 million and $60 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $357 million at December 31, 2018.

[2] Current and noncurrent assets are shown net of collateral of $169 million and $53 million, respectively, and current and noncurrent liabilities are shown net of collateral of $167 million and $77 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $466 million at December 31, 2017.