Derivative Financial Instruments - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Cash Collateral Posted	$ 37,000
Letters of credit posted	19,000
Exelon Generation Co L L C [Member]
Derivative [Line Items]
Cash collateral received not offset against net derivative positions	(6,000)	$ 2,000
Cash Collateral Posted	542,000	418,000
Letters of credit held	26,000	44,000
Letters of credit posted	289,000	367,000
Cash collateral held	56,000	47,000
Incremental collateral for loss of investment grade credit rating	1,900,000	2,100,000
Commonwealth Edison Co [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating	8,000
Credit Exposure Under Off System Sales	$ 2,000
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
Baltimore Gas and Electric Company [Member]
Derivative [Line Items]
Incremental collateral for loss of investment grade credit rating	46,000
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	90.00%
Expected Generation Hedged In Year Two	64.00%
Expected generation hedged in year three	38.00%
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	93.00%
Expected Generation Hedged In Year Two	67.00%
Expected generation hedged in year three	41.00%
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	19000000
Energy Related Derivative [Member] | Commonwealth Edison Company [Member]
Derivative [Line Items]
Credit Derivative, Collateral Held Directly or by Third Parties	11000000
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	31000000
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Cash collateral received not offset against net derivative positions		12,000
Net receivable from electric utility	$ 36,000
PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from affiliated electric and gas utility	31,000
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	27,000
Potomac Electric Power Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	37,000
Delmarva Power and Light Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	5,000
Atlantic City Electric Company [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Net receivable from electric utility	4,000
Not Designated as Hedging Instrument, Economic Hedge [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Notional Amount	1,419,000	1,420,000
Not Designated as Hedging Instrument, Economic Hedge [Member] | Interest Rate Swap [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Notional Amount	619,000	620,000
Not Designated as Hedging Instrument, Economic Hedge [Member] | Foreign Exchange Contract [Member] | Exelon Generation Co L L C [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 209,000	$ 268,000