Related Party Transactions - Related Party Transactions included in Consolidated Balance Sheet (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended		0 Months Ended	12 Months Ended
	Dec. 31, 2014		Apr. 01, 2014	Dec. 31, 2013		Dec. 31, 2012
Related Party Transaction [Line Items]
Total payables to affiliates (current)	$ (8)			$ (116)
Long-term debt to financing trusts	648			648
Required purchases of power from CENG's nuclear plants not sold to third parties	85.00%
Purchase of nuclear output of CENG	50.01%
Purchase of nuclear output by EDF	49.99%
CENG Equity Investment Income Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	0	[1]		3	[1]
ComEd Financing Three Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	(4)			(4)
Long-term debt to financing trusts	206			206
PECO Trust Three Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	(1)			(1)
Long-term debt to financing trusts	81			81
PECO Trust Four Affiliate [Member]
Related Party Transaction [Line Items]
Long-term debt to financing trusts	103			103
BGE Capital Trust II [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	(3)			(4)
Long-term debt to financing trusts	258			258
Constellation Energy Nuclear Group Llc Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	0	[1]		3	[1]
Total payables to affiliates (current)	0	[2]		(85)	[2]
Keystone Fuels LLC Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	0	[3]		(12)	[3]
Conemaugh Fuels LLC Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	0	[3]		(9)	[3]
Other Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	0			(1)
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	113			108
Total payables to affiliates (current)	(107)			(181)
Total payables to affiliates (noncurrent)	2,880			2,740
Required purchases of power from CENG's nuclear plants not sold to third parties	85.00%		85.00%
Purchase of nuclear output by EDF			49.99%
Exelon Generation Co L L C [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	43	[4]		38	[4]
Total payables to affiliates (current)	(12)			0
Total payables to affiliates (noncurrent)	2,389	[5]		2,293	[5]
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group Llc Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	0	[2]		(85)	[2]
Exelon Generation Co L L C [Member] | Keystone Fuels LLC Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	0	[3]		(12)	[3]
Exelon Generation Co L L C [Member] | Conemaugh Fuels LLC Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	0	[3]		(9)	[3]
Exelon Generation Co L L C [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	1			2
Total payables to affiliates (current)	0			(2)
Exelon Generation Co L L C [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	29	[6]		38	[6]
Total payables to affiliates (noncurrent)	490	[5]		447	[5]
Exelon Generation Co L L C [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	40	[7]		27	[7]
Exelon Generation Co L L C [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	(12)	[8]		(7)	[8]
Exelon Generation Co L L C [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	(83)	[9]		(66)	[9]
Total payables to affiliates (noncurrent)	1	[9]		0	[9]
Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	(66)			(55)
Prepaid voluntary employee beneficiary association trust	1	[10]		1	[10]
Baltimore Gas and Electric Company [Member] | BGE Capital Trust II [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	(3)			(4)
Long-term debt to financing trusts	258			258
Baltimore Gas and Electric Company [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	(1)			(3)
Baltimore Gas and Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	(40)	[11]		(27)	[11]
Baltimore Gas and Electric Company [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	(5)	[10]		(1)	[10]
Baltimore Gas and Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	(17)	[12]		(20)	[12]
PECO Energy Co [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	3			3
Total receivable from affiliates (noncurrent)	490			447
Total payables to affiliates (current)	(52)			(58)
Long-term debt to financing trusts	184			184
Prepaid voluntary employee beneficiary association trust	3	[13]		3	[13]
PECO Energy Co [Member] | Commonwealth Edison Co Affiliate [Member]
Related Party Transaction [Line Items]
Total receivable from affiliates (noncurrent)	2			0
PECO Energy Co [Member] | PECO Trust Three Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	(1)			(1)
Long-term debt to financing trusts	81			81
PECO Energy Co [Member] | PECO Trust Four Affiliate [Member]
Related Party Transaction [Line Items]
Long-term debt to financing trusts	103			103
PECO Energy Co [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Total receivable from affiliates (noncurrent)	1			3
PECO Energy Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Total receivable from affiliates (noncurrent)	490	[14]		447	[14]
Total payables to affiliates (current)	(29)	[15]		(38)	[15]
PECO Energy Co [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	(2)			(2)
PECO Energy Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	(20)	[16]		(17)	[16]
Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	14			3
Total receivable from affiliates (noncurrent)	2,571			2,469
Total payables to affiliates (current)	(84)			(83)
Prepaid voluntary employee beneficiary association trust	13	[17]		13	[17]
Energy Contract Amortization				0	[18]	0	[18]
Commonwealth Edison Co [Member] | ComEd Financing Three Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	(4)			(4)
Long-term debt to financing trusts	206			206
Commonwealth Edison Co [Member] | Voluntary Employee Beneficiary Association Trust [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	2			3
Commonwealth Edison Co [Member] | Other Affiliate [Member]
Related Party Transaction [Line Items]
Total receivable from affiliates (noncurrent)	182	[19]		176	[19]
Total payables to affiliates (current)	0			(2)
Commonwealth Edison Co [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	(2)			0
Commonwealth Edison Co [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Total receivables from affiliates (current)	12			0
Commonwealth Edison Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Total receivable from affiliates (noncurrent)	2,389	[20]		2,293	[20]
Total payables to affiliates (current)	(43)	[21]		(38)	[21]
Commonwealth Edison Co [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	(3)			(9)
Commonwealth Edison Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Total payables to affiliates (current)	$ (32)	[22]		$ (30)	[22]

[1] Beginning in 2012, Generation entered into a power services agency agreement (PSAA) with the CENG plants, which as of April 1, 2014, was amended and extended until the permanent cessation of power generation by the CENG generation plants. The PSAA is an agreement under which Generation provides scheduling, asset management and billing services to the CENG plants for a specified monthly fee. The charges for services reflect the cost of the services. On April 1, 2014, Generation and CENG entered into a Nuclear Operating Services Agreement (NOSA) pursuant to which Generation will operate the CENG nuclear generation fleet owned by CENG subsidiaries and provide corporate and administrative services for the remaining life of the CENG nuclear plants as if they were part of the Generation nuclear fleet. For further information regarding the Investment in CENG, see Note 5—Investment in Constellation Energy Nuclear Group, LLC.

[2] CENG owns 100% of four nuclear units in Maryland and New York and 82% of Nine Mile Point Unit 2 in New York. Beginning in 2012, Generation had a PPA under which it purchased 85% of the nuclear plant output owned by CENG that was not sold to third parties under pre-existing unit-contingent PPAs through 2014. Beginning on January 1, 2015 and continuing to the end of the life of the respective plants, Generation will purchase on a unit-contingent basis 50.01% of the nuclear plant output owned by CENG and a subsidiary of EDF will purchase on a unit-contingent basis 49.99% of the nuclear plant output owned by CENG (EDF PPA). Beginning April 1, 2014, sales to Generation are eliminated in consolidation. For further information regarding the Investment in CENG, see Note 5—Investment in Constellation Energy Nuclear Group, LLC.

[3] During 2014, Generation closed the sale of Safe Harbor Water Power Corporation, Keystone Fuels, LLC, and Conemaugh Fuels LLC. Generation recorded purchase power and fuel costs from affiliates related to these generating assets during the time these assets were still partially owned by Generation. See Note 4—Mergers, Acquisitions, and Dispositions for more information.

[4] Generation has an ICC-approved RFP contract with ComEd to provide a portion of ComEd’s electricity supply requirements. Generation also sells RECs to ComEd. In addition, Generation had revenue from ComEd associated with the settled portion of the financial swap contract established as part of the Illinois Settlement. See Note 3—Regulatory Matters for additional information.

[5] Generation has long-term payables to ComEd and PECO as a result of the nuclear decommissioning contractual construct whereby, to the extent NDT funds are greater than the underlying ARO at the end of decommissioning, such amounts are due back to ComEd and PECO, as applicable, for payment to their respective customers. See Note 15—Asset Retirement Obligations

[6] Generation provides electric supply to PECO under contracts executed through PECO’s competitive procurement process. In addition, Generation has five-year and ten-year agreements with PECO to sell non-solar and solar AECs, respectively. See Note 3—Regulatory Matters for additional information.

[7] Generation provides a portion of BGE’s energy requirements under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.

[8] The balance consists of interest owed to Exelon Corporation related to the senior unsecured notes, as well as, expense related to certain invoices Exelon Corporation processed on behalf of Generation.

[9] Generation receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.

[10] The voluntary employee benefit association trusts covering active employees are included in corporate operations and are funded by the Registrants. A prepayment to the active welfare plans has accumulated due to actuarially determined contribution rates, which are the basis for BGE’s contributions to the plans, being higher than actual claim expense incurred by the plans over time. The prepayment is included in other current assets.

[11] BGE procures a portion of its electricity and gas supply requirements from Generation under its MDPSC-approved market-based SOS and gas commodity programs. See Note 3—Regulatory Matters for additional information.

[12] BGE receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.

[13] The voluntary employee beneficiary association trusts covering active employees are included in corporate operations and are funded by the Registrants. A prepayment to the active welfare plans has accumulated due to actuarially determined contribution rates, which are the basis for PECO’s contributions to the plans, being higher than actual claim expense incurred by the plans over time.

[14] PECO has a long-term receivable from Generation as a result of the nuclear decommissioning contractual construct, whereby, to the extent the assets associated with decommissioning are greater than the applicable ARO at the end of decommissioning, such amounts are due back to PECO for payment to PECO’s customers.

[15] PECO purchases electric supply from Generation under contracts executed through its competitive procurement process. In addition, PECO has five-year and ten-year agreements with Generation to purchase non-solar and solar AECs, respectively. See Note 3—Regulatory Matters for additional information on AECs.

[16] PECO receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.

[17] The voluntary employee benefit association trusts covering active employees are included in corporate operations and are funded by the Registrants. A prepayment to the active welfare plans has accumulated due to actuarially determined contribution rates, which are the basis for ComEd’s contributions to the plans, being higher than actual claim expense incurred by the plans over time. The prepayment is included in other current assets.

[18] Included in Operating revenues or Purchased power and fuel on the Registrants’ Consolidated Statements of Operations and Comprehensive Income.

[19] Represents indemnification from Exelon Corporate related to the like-kind exchange transaction.

[20] ComEd has a long-term receivable from Generation as a result of the nuclear decommissioning contractual construct for generating facilities previously owned by ComEd. To the extent the assets associated with decommissioning are greater than the applicable ARO at the end of decommissioning, such amounts are due back to ComEd for payment to ComEd’s customers.

[21] ComEd procures a portion of its electricity supply requirements from Generation under an ICC-approved RFP contract. ComEd also purchases RECs from Generation. In addition, purchased power expense includes the settled portion of the financial swap contract with Generation, which expired in 2013. See Note 3—Regulatory Matters and Note 12—Derivative Financial Instruments for additional information.

[22] ComEd receives a variety of corporate support services from BSC, including legal, human resources, financial, information technology and supply management services. All services are provided at cost, including applicable overhead. A portion of such services is capitalized.