Fair Value of Financial Assets and Liabilities - Fair Value of Financial Liabilities Recorded at the Carrying Amount (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt	$ 460		$ 341
Long-term debt (including amounts due within one year)	441		384
Long-term debt to financing trusts	648		648
Long-term debt to financing trusts	648		648
Spent Nuclear Fuel Obligation, Noncurrent	1,021		1,021
Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt	463		344
Long-term debt to financing trusts	648		648
Debt and Capital Lease Obligations	21,164		19,132
Spent Nuclear Fuel Obligation, Noncurrent	1,021		1,021
Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term liabilities	463		344
Long-term debt (including amounts due within one year)	22,936		19,751
Long-term debt to financing trusts	648		631
SNF obligation	833		790
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term liabilities	3
Long-term debt (including amounts due within one year)	1,208
Long-term debt to financing trusts	0
SNF obligation	0
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term liabilities	448
Long-term debt (including amounts due within one year)	20,417
Long-term debt to financing trusts	0
SNF obligation	833
Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term liabilities	12
Long-term debt (including amounts due within one year)	1,311
Long-term debt to financing trusts	648
SNF obligation	0
Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt	36		22
Long-term debt (including amounts due within one year)	146		166
Long-term debt to financing trusts	943		1,523
Debt and Capital Lease Obligations	7,652		7,168
Spent Nuclear Fuel Obligation, Noncurrent	1,021		1,021
Exelon Generation Co L L C [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt	36		22
Debt and Capital Lease Obligations	8,266		7,729
Spent Nuclear Fuel Obligation, Noncurrent	1,021		1,021
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term liabilities	36		22
Long-term debt (including amounts due within one year)	8,822		7,648
SNF obligation	833		790
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term liabilities	0
Long-term debt (including amounts due within one year)	0
SNF obligation	0
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term liabilities	24
Long-term debt (including amounts due within one year)	7,511
SNF obligation	833
Exelon Generation Co L L C [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term liabilities	12
Long-term debt (including amounts due within one year)	1,311
SNF obligation	0
Commonwealth Edison Co [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt	304		184
Long-term debt to financing trusts	206		206
Debt and Capital Lease Obligations	5,698		5,058
Commonwealth Edison Co [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt	304		184
Long-term debt to financing trusts	206		206
Debt and Capital Lease Obligations	5,958		5,675
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term liabilities	304		184
Long-term debt (including amounts due within one year)	6,788		6,255
Long-term debt to financing trusts	213		202
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term liabilities	0
Long-term debt (including amounts due within one year)	0
Long-term debt to financing trusts	0
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term liabilities	304
Long-term debt (including amounts due within one year)	6,788
Long-term debt to financing trusts	0
Commonwealth Edison Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term liabilities	0
Long-term debt (including amounts due within one year)	0
Long-term debt to financing trusts	213
PECO Energy Co [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt to financing trusts	184	[1]	184	[1]
Debt and Capital Lease Obligations	2,246		1,947
Long-term debt to financing trusts	184		184
PECO Energy Co [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt to financing trusts	184		184
Debt and Capital Lease Obligations	2,246		2,197
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)	2,537		2,358
Long-term debt to financing trusts	199		180
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)	0
Long-term debt to financing trusts	0
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)	2,537
Long-term debt to financing trusts	0
PECO Energy Co [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt (including amounts due within one year)	0
Long-term debt to financing trusts	199
Baltimore Gas and Electric Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt	120		135
Long-term debt to financing trusts	258		258
Debt and Capital Lease Obligations			2,011
Baltimore Gas and Electric Company [Member] | Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term Debt	123		138
Long-term debt to financing trusts	258
Debt and Capital Lease Obligations	1,942
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term liabilities	123		138
Long-term debt (including amounts due within one year)	2,178		2,148
Long-term debt to financing trusts	236		249
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term liabilities	3
Long-term debt (including amounts due within one year)	0
Long-term debt to financing trusts	0
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term liabilities	120
Long-term debt (including amounts due within one year)	2,178
Long-term debt to financing trusts	0
Baltimore Gas and Electric Company [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term liabilities	0
Long-term debt (including amounts due within one year)	0
Long-term debt to financing trusts	$ 236

[1] Amounts owed to this financing trust are recorded as Long-term debt to financing trusts within PECO’s Consolidated Balance Sheets.