Fair Value of Financial Assets and Liabilities - Fair Value of Financial Liabilities Recorded at the Carrying Amount (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	$ 312	$ 463
Long-term debt (including amounts due within one year)	21,779	21,164
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	312	463
Long-term debt (including amounts due within one year)	23,985	22,936
Long-term debt to financing trusts	672	648
SNF obligation	843	833
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)	1,119	1,208
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	309	448
Long-term debt (including amounts due within one year)	21,486	20,417
Long-term debt to financing trusts	0	0
SNF obligation	843	833
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	0	12
Long-term debt (including amounts due within one year)	1,380	1,311
Long-term debt to financing trusts	672	648
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	25	36
Long-term debt (including amounts due within one year)	8,492	8,266
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	25	36
Long-term debt (including amounts due within one year)	9,265	8,822
SNF obligation	843	833
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	25	24
Long-term debt (including amounts due within one year)	7,885	7,511
SNF obligation	843	833
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	12
Long-term debt (including amounts due within one year)	1,380	1,311
SNF obligation	0	0
Commonwealth Edison Co [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	283	304
Long-term debt (including amounts due within one year)	6,359	5,958
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	283	304
Long-term debt (including amounts due within one year)	7,347	6,788
Long-term debt to financing trusts	206	213
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	283	304
Long-term debt (including amounts due within one year)	7,347	6,788
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	0
Long-term debt to financing trusts	206	213
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)	2,246	2,246
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)	2,602	2,537
Long-term debt to financing trusts	201	199
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)	2,602	2,537
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	201	199
Baltimore Gas and Electric Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term liabilities	3	123
Long-term debt (including amounts due within one year)	1,942	1,942
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	3	123
Long-term debt (including amounts due within one year)	2,234	2,178
Long-term debt to financing trusts	265	236
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	0	120
Long-term debt (including amounts due within one year)	2,234	2,178
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	$ 265	$ 236