Derivative Financial Instruments - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Derivative [Line Items]
Ineffective portion recognized in income	$ 6,000	$ 4,000
Cash collateral posted	41,000
Letters of credit posted	23,000
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Cash collateral received not offset against net derivative positions	(8,000)		$ 4,000
Cash collateral posted	742,000		497,000
Letters of credit held	46,000		33,000
Letters of credit posted	493,000		293,000
Cash collateral held	66,000		35,000
Incremental collateral for loss of investment grade credit rating	1,900,000		1,800,000
Interest Rate Fair Value Hedge Asset at Fair Value	13,000
Commonwealth Edison Co [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating	10,000
Credit Exposure Under Off System Sales	$ 1,000
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	$ 33,000
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating	49,000
Credit Exposure Under Off System Sales	12,000
Delmarva Power and Light Company [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating	$ 14,000
Minimum [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected Generation Hedged In Next Twelve Months	91.00%
Expected Generation Hedged In Year Two	63.00%
Expected generation hedged in year three	33.00%
Minimum [Member] | Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged	10.00%
Maximum [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Expected Generation Hedged In Next Twelve Months	94.00%
Expected Generation Hedged In Year Two	66.00%
Expected generation hedged in year three	36.00%
Maximum [Member] | Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Estimated percentage of natural gas purchases hedged	20.00%
Other Contract [Member] | Commonwealth Edison Company [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties	19
Foreign Exchange Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 87,000		94,000
Energy Related Derivative [Member] | Commonwealth Edison Company [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties	9
Energy Related Derivative [Member] | Delmarva Power and Light Company [Member]
Derivative [Line Items]
Brokered Natural Gas Margin Revenue	$ 2,750
Renewable Energy Program [Member] | Commonwealth Edison Company [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties	14
InterestRateAndForeignExchangeContract [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	$ 9,000		5,000
InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	13,000		2,000
Fair Value Hedging [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	800,000		800,000
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	31,000
PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from affiliated electric and gas utility	21,000
Baltimore Gas And Electric Company Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from affiliated electric and gas utility	25,000
Potomac Electric Power Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	34,000
Delmarva Power and Light Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	9,000
Atlantic City Electric Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	5,000
Designated as Hedging Instrument [Member] | InterestRateAndForeignExchangeContract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Fair Value, Net	12,000		1,000
Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 636,000		$ 636,000