Fair Value of Financial Assets and Liabilities - Fair Value of Financial Liabilities Recorded at the Carrying Amount (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt	$ 675	$ 460
Due to Related Parties, Noncurrent	648	648
Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt	678	463
Long-term debt (including amounts due within one year)	25,438	21,164
SNF obligation	1,021	1,021
Due to Related Parties, Noncurrent	648	648
Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Lines of Credit, Fair Value Disclosure	678	463
Long-term debt (including amounts due within one year)	26,520	22,936
SNF obligation	820	833
Due to Related Parties, Noncurrent	663	648
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Lines of Credit, Fair Value Disclosure	3	3
Long-term debt (including amounts due within one year)	1,004	1,208
SNF obligation	0	0
Due to Related Parties, Noncurrent	0	0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Lines of Credit, Fair Value Disclosure	675	448
Long-term debt (including amounts due within one year)	24,181	20,417
SNF obligation	820	833
Due to Related Parties, Noncurrent	0	0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Lines of Credit, Fair Value Disclosure	0	12
Long-term debt (including amounts due within one year)	1,335	1,311
SNF obligation	0	0
Due to Related Parties, Noncurrent	663	648
Exelon Generation Co L L C [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt	21	36
Exelon Generation Co L L C [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt	21	36
Long-term debt (including amounts due within one year)	8,996	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]
Lines of Credit, Fair Value Disclosure	21	36
Long-term debt (including amounts due within one year)	9,313	8,822
SNF obligation	820	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]
Lines of Credit, Fair Value Disclosure	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]
Lines of Credit, Fair Value Disclosure	21	24
Long-term debt (including amounts due within one year)	7,978	7,511
SNF obligation	820	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]
Lines of Credit, Fair Value Disclosure	0	12
Long-term debt (including amounts due within one year)	1,335	1,311
SNF obligation	0	0
Commonwealth Edison Co [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt	604	304
Due to Related Parties, Noncurrent	206	206
Commonwealth Edison Co [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt	604	304
Long-term debt (including amounts due within one year)	6,100	5,958
Due to Related Parties, Noncurrent	206	206
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Lines of Credit, Fair Value Disclosure	604	304
Long-term debt (including amounts due within one year)	6,731	6,788
Due to Related Parties, Noncurrent	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]
Lines of Credit, Fair Value Disclosure	0	0
Long-term debt (including amounts due within one year)	0	0
Due to Related Parties, Noncurrent	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]
Lines of Credit, Fair Value Disclosure	604	304
Long-term debt (including amounts due within one year)	6,731	6,788
Due to Related Parties, Noncurrent	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]
Lines of Credit, Fair Value Disclosure	0	0
Long-term debt (including amounts due within one year)	0	0
Due to Related Parties, Noncurrent	206	213
PECO Energy Co [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Due to Related Parties, Noncurrent	184	184
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
Due to Related Parties, Noncurrent	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)	2,472	2,537
Due to Related Parties, Noncurrent	196	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
Due to Related Parties, Noncurrent	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)	2,472	2,537
Due to Related Parties, Noncurrent	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
Due to Related Parties, Noncurrent	196	199
Baltimore Gas and Electric Company [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt	50	120
Due to Related Parties, Noncurrent	258	258
Baltimore Gas and Electric Company [Member] | Reported Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Short-term Debt	53	123
Long-term debt (including amounts due within one year)	1,905	1,942
Due to Related Parties, Noncurrent	258	258
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member]
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Lines of Credit, Fair Value Disclosure	53	123
Long-term debt (including amounts due within one year)	2,118	2,178
Due to Related Parties, Noncurrent	261	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]
Lines of Credit, Fair Value Disclosure	3	3
Long-term debt (including amounts due within one year)	0	0
Due to Related Parties, Noncurrent	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]
Lines of Credit, Fair Value Disclosure	50	120
Long-term debt (including amounts due within one year)	2,118	2,178
Due to Related Parties, Noncurrent	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]
Lines of Credit, Fair Value Disclosure	0	0
Long-term debt (including amounts due within one year)	0	0
Due to Related Parties, Noncurrent	$ 261	$ 236