Debt and Credit Agreements - Summary of Credit Facility Thresholds (Details)	12 Months Ended
	Dec. 31, 2017
Line of Credit Facility [Line Items]
Credit agreement threshold	2.50
Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	27.50%
London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	12750.00%
Exelon Generation Co L L C [Member]
Line of Credit Facility [Line Items]
Credit agreement threshold	3.00
Exelon Generation Co L L C [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	27.50%
Exelon Generation Co L L C [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	12750.00%
Commonwealth Edison Co [Member]
Line of Credit Facility [Line Items]
Credit agreement threshold	2.00
Commonwealth Edison Co [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	7.50%
Commonwealth Edison Co [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	10750.00%
PECO Energy Co [Member]
Line of Credit Facility [Line Items]
Credit agreement threshold	2.00
PECO Energy Co [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	0.00%
PECO Energy Co [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	9000.00%
Baltimore Gas and Electric Company [Member]
Line of Credit Facility [Line Items]
Credit agreement threshold	2.00
Baltimore Gas and Electric Company [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	0.00%
Baltimore Gas and Electric Company [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	10000.00%
Potomac Electric Power Company [Member]
Line of Credit Facility [Line Items]
Credit agreement threshold	2.00
Potomac Electric Power Company [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	7.50%
Potomac Electric Power Company [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	10750.00%
Delmarva Power and Light Company [Member]
Line of Credit Facility [Line Items]
Credit agreement threshold	2.00
Delmarva Power and Light Company [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	7.50%
Delmarva Power and Light Company [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	10750.00%
Atlantic City Electric Company [Member]
Line of Credit Facility [Line Items]
Credit agreement threshold	2.00
Atlantic City Electric Company [Member] | Prime Rate [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	7.50%
Atlantic City Electric Company [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	10750.00%