Related Party Transactions - Related Party Transactions included in Consolidated Income Statement (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended						0 Months Ended	3 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012		Apr. 01, 2014	Mar. 11, 2012
Related Party Transaction [Line Items]
Operating revenues from affiliates									$ 23		$ 70		$ 48
Revenues	7,255	6,912	6,024	7,237	6,163	6,502	6,141	6,082	27,429	[1]	24,888	[1]	23,489	[1]
Purchase power and fuel from affiliates									531		1,256		1,036
Total interest expense to affiliates, net									41		41		37
Total income (loss) in equity method investments									(20)		10		(91)
Cash dividends paid to parent									1,065		1,249		1,716
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%
PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates									1	[2]	10	[2]	6	[2]
Constellation Energy Nuclear Group Llc Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates									17	[3]	56	[3]	42	[3]
Purchase power and fuel from affiliates									282	[4]	992	[4]	793	[4]
Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates									5		4		0
Keystone Fuels LLC Affiliate [Member]
Related Party Transaction [Line Items]
Purchase power and fuel from affiliates									138	[5]	144	[5]	119	[5]
Conemaugh Fuels LLC Affiliate [Member]
Related Party Transaction [Line Items]
Purchase power and fuel from affiliates									99	[5]	98	[5]	101	[5]
SafeHarborWaterPowerCorp [Member]
Related Party Transaction [Line Items]
Purchase power and fuel from affiliates									12	[5]	22	[5]	23	[5]
ComEd Financing Three Affiliate [Member]
Related Party Transaction [Line Items]
Total interest expense to affiliates, net									13		13		13
PECO Trust Three Affiliate [Member]
Related Party Transaction [Line Items]
Total interest expense to affiliates, net									6		6		6
PECO Trust Four Affiliate [Member]
Related Party Transaction [Line Items]
Total interest expense to affiliates, net									6		6		6
BGE Capital Trust II [Member]
Related Party Transaction [Line Items]
Total interest expense to affiliates, net									16	[6]	16	[6]	12	[6]
CENG Equity Investment Income Affiliate [Member]
Related Party Transaction [Line Items]
Total income (loss) in equity method investments									(19)	[7]	9	[7]	(99)	[7]
Other Affiliate [Member]
Related Party Transaction [Line Items]
Total income (loss) in equity method investments									(1)		1		8
Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates									779		1,423		1,702
Revenues	4,802	4,412	3,789	4,390	3,772	4,255	4,070	3,533	17,393		15,630		14,437
Purchase power and fuel from affiliates									557		1,270		1,044
Operating and maintenance from affiliates									623		574		630
Total interest expense to affiliates, net									53		59		75
Total income (loss) in equity method investments									(20)		10		(91)
Cash distribution paid to member									645		625		1,626
Contribution from member									53		26		48
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]
Operating revenues from affiliates											506	[8]	795	[8]
Revenues									176	[8]
Purchase power and fuel from affiliates									1		1		0
Operating and maintenance from affiliates									3	[9]	2	[9]	2	[9]
Exelon Generation Co L L C [Member] | PECO Energy Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates											405	[10]	543	[10]
Revenues									198	[10]
Operating and maintenance from affiliates									2	[9]	1	[9]	3	[9]
Exelon Generation Co L L C [Member] | Baltimore Gas And Electric Company Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates											455	[11]	322	[11]
Revenues									387	[11]
Purchase power and fuel from affiliates									25		13		8
Exelon Generation Co L L C [Member] | Constellation Energy Nuclear Group Llc Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates									17	[3]	56	[3]	42	[3]
Purchase power and fuel from affiliates									282	[4]	992	[4]	793	[4]
Exelon Generation Co L L C [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates									1		1		0
Operating and maintenance from affiliates									618	[12]	571	[12]	625	[12]
Capitalized Costs									91	[13]	93	[13]	80	[13]
Exelon Generation Co L L C [Member] | Exelon Corporation Affiliate [Member]
Related Party Transaction [Line Items]
Total interest expense to affiliates, net									53		59		75
Exelon Generation Co L L C [Member] | Keystone Fuels LLC Affiliate [Member]
Related Party Transaction [Line Items]
Purchase power and fuel from affiliates									138	[5]	144	[5]	119	[5]
Exelon Generation Co L L C [Member] | Conemaugh Fuels LLC Affiliate [Member]
Related Party Transaction [Line Items]
Purchase power and fuel from affiliates									99	[5]	98	[5]	101	[5]
Exelon Generation Co L L C [Member] | SafeHarborWaterPowerCorp [Member]
Related Party Transaction [Line Items]
Purchase power and fuel from affiliates									12		22		23
Exelon Generation Co L L C [Member] | CENG Equity Investment Income Affiliate [Member]
Related Party Transaction [Line Items]
Total income (loss) in equity method investments									(19)	[14]	9	[14]	(99)	[14]
Exelon Generation Co L L C [Member] | Qualifying Facilities And Domestic Power Projects Affiliate [Member]
Related Party Transaction [Line Items]
Total income (loss) in equity method investments									(1)		1		8
Exelon Generation Co L L C [Member] | Exelon Generation Co L L C [Member]
Related Party Transaction [Line Items]
Total income (loss) in equity method investments									(20)
Commonwealth Edison Co [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates									4		3		2
Revenues	1,079	1,222	1,128	1,134	1,068	1,156	1,080	1,160	4,564		4,464		5,443
Operating and maintenance from affiliates									166		157		163
Total interest expense to affiliates, net									13		13		13
Total income (loss) in equity method investments									0		0
Cash dividends paid to parent									307		220		105
Non-cash contribution to equity									273		0		11
Contributions from parent									273		0		0
Amortization of energy contract assets and liabilities											0	[15]	0	[15]
Commonwealth Edison Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates									4		3		2
Purchase power and fuel from affiliates									176	[16]	512	[16]	789	[16]
Commonwealth Edison Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates									166	[13]	157	[13]	163	[13]
Capitalized Costs									77	[13]	69	[13]	92	[13]
Commonwealth Edison Co [Member] | ComEd Financing Three Affiliate [Member]
Related Party Transaction [Line Items]
Total interest expense to affiliates, net									13		13		13
Baltimore Gas and Electric Company [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates									25		13		10
Revenues	761	697	653	1,054	794	737	653	880	3,165		3,065		2,735
Operating and maintenance from affiliates									103		83		106
Total interest expense to affiliates, net									16		16		16			4
Total income (loss) in equity method investments									0		0		0
Contributions from parent									0		0		66
Baltimore Gas and Electric Company [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates									25	[17]	13	[17]	10	[17]
Purchase power and fuel from affiliates									382	[18]	452	[18]	396	[18]
Baltimore Gas and Electric Company [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates									103	[19]	83	[19]	106	[19]
Capitalized Costs									19	[19]	15	[19]	21	[19]
Baltimore Gas and Electric Company [Member] | BGE Capital Trust II [Member]
Related Party Transaction [Line Items]
Total interest expense to affiliates, net									16		16		16
PECO Energy Co [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates									2		1		3
Revenues	750	693	656	993	805	728	672	895	3,094		3,100		3,186
Operating and maintenance from affiliates									99		101		111
Total interest expense to affiliates, net									12		12		12
Total income (loss) in equity method investments									0		0		0
Cash dividends paid to parent									320		332		343
Contributions from parent									24		27		9
PECO Energy Co [Member] | Exelon Generation Co LLC Affiliate [Member]
Related Party Transaction [Line Items]
Operating revenues from affiliates									2	[20]	1	[20]	3	[20]
Purchase power and fuel from affiliates									194	[21]	392	[21]	533	[21]
Operating and maintenance from affiliates									3		3		4
PECO Energy Co [Member] | Exelon Business Services Co Affiliate [Member]
Related Party Transaction [Line Items]
Operating and maintenance from affiliates									96	[22]	98	[22]	107	[22]
Capitalized Costs									39	[22]	46	[22]	54	[22]
PECO Energy Co [Member] | PECO Trust Three Affiliate [Member]
Related Party Transaction [Line Items]
Total interest expense to affiliates, net									6		6		6
PECO Energy Co [Member] | PECO Trust Four Affiliate [Member]
Related Party Transaction [Line Items]
Total interest expense to affiliates, net									$ 6		$ 6		$ 6

[1] For the years ended December 31, 2014, 2013 and 2012, utility taxes of $89 million, $79 million and $82 million, respectively, are included in revenues and expenses for Generation. For the years ended December 31, 2014, 2013 and 2012, utility taxes of $238 million, $241 million and $239 million, respectively, are included in revenues and expenses for ComEd. For the years ended December 31, 2014, 2013 and 2012, utility taxes of $128 million, $129 million and $141 million, respectively, are included in revenues and expenses for PECO. For the years ended December 31, 2014, December 31, 2013 and for the period of March 12, 2012 through December 31, 2012, utility taxes of $86 million, $82 million and $59 million are included in revenues and expenses for BGE, respectively.

[2] The intersegment profit associated with the sale of certain products and services by and between Exelon’s segments is not eliminated in consolidation due to the recognition of intersegment profit in accordance with regulatory accounting guidance. For Exelon, these amounts are included in operating revenues in the Consolidated Statement of Operations. See Note 3—Regulatory Matters for additional information.

[3] 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.

[4] 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.

[5] 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.

[6] The BGE Capital Trust II portion of Exelon’s interest expense to affiliates, net, for December 31, 2012 excludes $4 million of expense incurred in 2012 prior to the closing of Exelon’s merger with Constellation on March 12, 2012.

[7] Prior to April 1, 2014, Generation’s total gain (loss) in equity method investments includes equity investment income (loss) and amortization of the basis difference established as a result of purchase accounting applied upon Constellation merger in 2012. CENG was fully consolidated on April 1, 2014. For further information regarding the Investment in CENG, see Note 5—Investment in Constellation Energy Nuclear Group, LLC

[8] 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.

[9] Generation requires electricity for its own use at its generating stations. Generation purchases electricity and distribution and transmission services from PECO and only distribution and transmission services from ComEd for the delivery of electricity to its generating stations.

[10] 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.

[11] 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.

[12] 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.

[13] 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.

[14] Prior to April 1, 2014, Generation’s total gain (loss) in equity method investments includes equity income (loss) and amortization of the basis difference established as a result of purchase accounting applied upon Constellation merger in 2012. CENG was fully consolidated on April 1, 2014. For further information regarding the Investment in CENG, see Note 5—Investment in Constellation Energy Nuclear Group, LLC.

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

[16] 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.

[17] BGE provides energy to Generation for Generation’s own use.

[18] 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.

[19] 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.

[20] PECO provides energy to Generation for Generation’s own use.

[21] 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.

[22] 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.