Fair Value of Financial Assets and Liabilities - Fair Value of Financial Liabilities Recorded at the Carrying Amount (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	$ 565	$ 344
Long-term debt (including amounts due within one year)	21,264	19,132
Long-term debt to financing trusts	648	648
SNF obligation	1,021	1,021
Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	565	344
Long-term debt (including amounts due within one year)	22,743	19,751
Long-term debt to financing trusts	677	631
SNF obligation	849	790
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	3	3
Long-term debt (including amounts due within one year)	1,168	0
Long-term debt to financing trusts	0	0
SNF obligation	0	0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	562	341
Long-term debt (including amounts due within one year)	20,278	18,672
Long-term debt to financing trusts	0	0
SNF obligation	849	790
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	0	0
Long-term debt (including amounts due within one year)	1,297	1,079
Long-term debt to financing trusts	677	631
SNF obligation	0	0
Exelon Generation Co L L C [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	14	22
Long-term debt (including amounts due within one year)	8,320	7,729
SNF obligation	1,021	1,021
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	14	22
Long-term debt (including amounts due within one year)	8,840	7,648
SNF obligation	849	790
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	0	0
Long-term debt (including amounts due within one year)	0	0
SNF obligation	0	0
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	14	22
Long-term debt (including amounts due within one year)	7,543	6,586
SNF obligation	849	790
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	0	0
Long-term debt (including amounts due within one year)	1,297	1,062
SNF obligation	0	0
Commonwealth Edison Co [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	528	184
Long-term debt (including amounts due within one year)	5,708	5,675
Long-term debt to financing trusts	206	206
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	528	184
Long-term debt (including amounts due within one year)	6,422	6,255
Long-term debt to financing trusts	214	202
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	0	0
Long-term debt (including amounts due within one year)	0	0
Long-term debt to financing trusts	0	0
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	528	184
Long-term debt (including amounts due within one year)	6,422	6,238
Long-term debt to financing trusts	0	0
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	0	0
Long-term debt (including amounts due within one year)	0	17
Long-term debt to financing trusts	214	202
PECO Energy Co [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	2,496	2,197
Long-term debt to financing trusts	184	184
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	2,720	2,358
Long-term debt to financing trusts	204	180
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	0	0
Long-term debt to financing trusts	0	0
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	2,720	2,358
Long-term debt to financing trusts	0	0
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt (including amounts due within one year)	0	0
Long-term debt to financing trusts	204	180
Baltimore Gas and Electric Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	23	138
Long-term debt (including amounts due within one year)	1,976	2,011
Long-term debt to financing trusts	258	258
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	23	138
Long-term debt (including amounts due within one year)	2,196	2,148
Long-term debt to financing trusts	259	249
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	3	3
Long-term debt (including amounts due within one year)	0	0
Long-term debt to financing trusts	0	0
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	20	135
Long-term debt (including amounts due within one year)	2,196	2,148
Long-term debt to financing trusts	0	0
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	0	0
Long-term debt (including amounts due within one year)	0	0
Long-term debt to financing trusts	$ 259	$ 249