Commitments and Contingencies - Schedule of Commercial Commitments (Details) (USD $)	Dec. 31, 2014
Guarantor Obligations [Line Items]
Total	$ 9,402,000,000
2015	5,448,000,000
2016	107,000,000
2017	29,000,000
2018	21,000,000
2019	22,000,000
2020 and beyond	3,775,000,000
Percentage ownership of common stock	100.00%
Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Total	1,233,000,000	[1]
2015	1,151,000,000	[1]
2016	77,000,000	[1]
2017	5,000,000	[1]
2018	0	[1]
2019	0	[1]
2020 and beyond	0	[1]
Surety Bond [Member]
Guarantor Obligations [Line Items]
Total	596,000,000	[2]
2015	545,000,000	[2]
2016	10,000,000	[2]
2017	4,000,000	[2]
2018	1,000,000	[2]
2019	2,000,000	[2]
2020 and beyond	34,000,000	[2]
Performance Guarantee [Member]
Guarantor Obligations [Line Items]
Total	1,239,000,000	[3]
2015	472,000,000	[2]
2016	20,000,000	[2]
2017	20,000,000	[2]
2018	20,000,000	[2]
2019	20,000,000	[2]
2020 and beyond	687,000,000	[2]
Energy Contract Guarantee [Member]
Guarantor Obligations [Line Items]
Total	3,220,000,000	[4]
2015	3,220,000,000	[4]
2016	0	[4]
2017	0	[4]
2018	0	[4]
2019	0	[4]
2020 and beyond	0	[4]
Estimated total assumed for commercial transaction obligations	3,200,000,000
Property Lease Guarantee [Member]
Guarantor Obligations [Line Items]
Total	40,000,000	[5]
2015	0	[5]
2016	0	[5]
2017	0	[5]
2018	0	[5]
2019	0	[5]
2020 and beyond	40,000,000	[5]
Nuclear Insurance Premiums [Member]
Guarantor Obligations [Line Items]
Total	3,014,000,000	[6]
2015	0	[6]
2016	0	[6]
2017	0	[6]
2018	0	[6]
2019	0	[6]
2020 and beyond	3,014,000,000	[6]
Underwriters Discount [Member]
Guarantor Obligations [Line Items]
Total	60,000,000	[7]
2015	60,000,000	[7]
2016	0	[7]
2017	0	[7]
2018	0	[7]
2019	0	[7]
2020 and beyond	0	[7]
Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]
Guarantor Obligations [Line Items]
Estimated net exposure for commercial transaction obligations	600,000,000
Baltimore Gas and Electric Company [Member]
Guarantor Obligations [Line Items]
Total	265,000,000
2015	15,000,000
2016	0
2017	0
2018	0
2019	0
2020 and beyond	250,000,000
Baltimore Gas and Electric Company [Member] | Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Total	1,000,000	[8]
2015	1,000,000	[8]
2016	0	[8]
2017	0	[8]
2018	0	[8]
2019	0	[8]
2020 and beyond	0	[8]
Baltimore Gas and Electric Company [Member] | Surety Bond [Member]
Guarantor Obligations [Line Items]
Total	11,000,000	[9]
2015	11,000,000	[9]
2016	0	[9]
2017	0	[9]
2018	0	[9]
2019	0	[9]
2020 and beyond	0	[9]
Baltimore Gas and Electric Company [Member] | Performance Guarantee [Member]
Guarantor Obligations [Line Items]
Total	253,000,000	[10]
2015	3,000,000	[10]
2016	0	[10]
2017	0	[10]
2018	0	[10]
2019	0	[10]
2020 and beyond	250,000,000	[10]
Baltimore Gas and Electric Company [Member] | Trust Preferred Securities [Member]
Guarantor Obligations [Line Items]
Total	250,000,000
PECO Energy Co [Member]
Guarantor Obligations [Line Items]
Total	218,000,000
2015	40,000,000
2016	0
2017	0
2018	0
2019	0
2020 and beyond	178,000,000
PECO Energy Co [Member] | Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Total	22,000,000	[11]
2015	22,000,000	[11]
2016	0	[11]
2017	0	[11]
2018	0	[11]
2019	0	[11]
2020 and beyond	0	[11]
PECO Energy Co [Member] | Surety Bond [Member]
Guarantor Obligations [Line Items]
Total	18,000,000	[2]
2015	18,000,000	[2]
2016	0	[2]
2017	0	[2]
2018	0	[2]
2019	0	[2]
2020 and beyond	0	[2]
PECO Energy Co [Member] | Performance Guarantee [Member]
Guarantor Obligations [Line Items]
Total	178,000,000	[12]
2015	0	[12]
2016	0	[12]
2017	0	[12]
2018	0	[12]
2019	0	[12]
2020 and beyond	178,000,000	[12]
PECO Energy Co [Member] | Trust Preferred Securities [Member]
Guarantor Obligations [Line Items]
Total	178,000,000
Commonwealth Edison Co [Member]
Guarantor Obligations [Line Items]
Total	222,000,000
2015	20,000,000
2016	0
2017	0
2018	0
2019	0
2020 and beyond	202,000,000
Commonwealth Edison Co [Member] | Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Total	17,000,000	[13]
2015	17,000,000	[13]
2016	0	[13]
2017	0	[13]
2018	0	[13]
2019	0	[13]
2020 and beyond	0	[13]
Commonwealth Edison Co [Member] | Surety Bond [Member]
Guarantor Obligations [Line Items]
Total	5,000,000	[2]
2015	3,000,000	[2]
2016	0	[2]
2017	0	[2]
2018	0	[2]
2019	0	[2]
2020 and beyond	2,000,000	[2]
Commonwealth Edison Co [Member] | Performance Guarantee [Member]
Guarantor Obligations [Line Items]
Total	200,000,000	[14]
2015	0	[14]
2016	0	[14]
2017	0	[14]
2018	0	[14]
2019	0	[14]
2020 and beyond	200,000,000	[14]
Commonwealth Edison Co [Member] | Trust Preferred Securities [Member]
Guarantor Obligations [Line Items]
Total	200,000,000
Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Total	6,384,000,000
2015	3,137,000,000
2016	99,000,000
2017	25,000,000
2018	20,000,000
2019	20,000,000
2020 and beyond	3,083,000,000
Exelon Generation Co L L C [Member] | Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Total	1,187,000,000	[15]
2015	1,106,000,000	[15]
2016	76,000,000	[15]
2017	5,000,000	[15]
2018	0	[15]
2019	0	[15]
2020 and beyond	0	[15]
Exelon Generation Co L L C [Member] | Surety Bond [Member]
Guarantor Obligations [Line Items]
Total	481,000,000
2015	468,000,000
2016	3,000,000
2017	0
2018	0
2019	0
2020 and beyond	10,000,000
Exelon Generation Co L L C [Member] | Performance Guarantee [Member]
Guarantor Obligations [Line Items]
Total	458,000,000	[16]
2015	319,000,000	[16]
2016	20,000,000	[16]
2017	20,000,000	[16]
2018	20,000,000	[16]
2019	20,000,000	[16]
2020 and beyond	59,000,000	[16]
Exelon Generation Co L L C [Member] | Energy Contract Guarantee [Member]
Guarantor Obligations [Line Items]
Total	1,244,000,000	[17]
2015	1,244,000,000	[17]
2016	0	[17]
2017	0	[17]
2018	0	[17]
2019	0	[17]
2020 and beyond	0	[17]
Estimated total assumed for commercial transaction obligations	1,200,000,000
Exelon Generation Co L L C [Member] | Nuclear Insurance Premiums [Member]
Guarantor Obligations [Line Items]
Total	3,014,000,000	[18]
2015	0	[18]
2016	0	[18]
2017	0	[18]
2018	0	[18]
2019	0	[18]
2020 and beyond	3,014,000,000	[18]
Exelon Generation Co L L C [Member] | Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]
Guarantor Obligations [Line Items]
Estimated net exposure for commercial transaction obligations	$ 400,000,000
Commonwealth Edison Three [Member] | Commonwealth Edison Co [Member]
Guarantor Obligations [Line Items]
Percentage ownership of common stock	100.00%
PECO Trust III and IV [Member] | PECO Energy Co [Member]
Guarantor Obligations [Line Items]
Percentage ownership of common stock	100.00%

[1] Letters of credit (non-debt)—Exelon and certain of its subsidiaries maintain non-debt letters of credit to provide credit support for certain transactions as requested by third parties.

[2] Surety bonds—Guarantees issued related to contract and commercial agreements, excluding bid bonds.

[3] Performance guarantees—Guarantees issued to ensure performance under specific contracts. Additionally includes $200 million of Trust Preferred Securities of ComEd Financing III, $178 million of Trust Preferred Securities of PECO Trust III and IV and $250 million of Trust Preferred Securities of BGE Capital Trust II.

[4] Energy marketing contract guarantees—Guarantees issued to ensure performance under energy commodity contracts. Amount includes approximately $3.2 billion of guarantees previously issued by Constellation on behalf of its Generation and NewEnergy business to allow it the flexibility needed to conduct business with counterparties without having to post other forms of collateral. The majority of these guarantees contain evergreen provisions that require the guarantee to remain in effect until cancelled. Exelon’s estimated net exposure for obligations under commercial transactions covered by these guarantees is approximately $0.6 billion at December 31, 2014, which represents the total amount Exelon could be required to fund based on December 31, 2014 market prices.

[5] Lease guarantees—Guarantees issued to ensure payments on building leases.

[6] Nuclear insurance premiums—Represents the maximum amount that Generation would be required to pay for retrospective premiums in the event of nuclear disaster at any domestic site under the Secondary Financial Protection pool as required under the Price-Anderson Act as well as the current aggregate annual retrospective premium obligation that could be imposed by NEIL. See the Nuclear Insurance section within this note for additional details on Generation’s nuclear insurance premiums.

[7] Represents the underwriters discount for Exelon’s forward equity transaction. See Note 19 - Common Stock for further details of the equity securities offering.

[8] Letters of credit (non-debt)—BGE maintains non-debt letters of credit to provide credit support for certain transactions as requested by third parties.

[9] Surety bond—Guarantees issued related to contract and commercial agreements, excluding bid bonds.

[10] Performance guarantee—Reflects full and unconditional guarantee of Trust Preferred Securities of BGE Capital Trust which is an unconsolidated VIE of BGE.

[11] Letters of credit (non-debt)—PECO maintains non-debt letters of credit to provide credit support for certain transactions as requested by third parties.

[12] Performance guarantees—Reflects full and unconditional guarantee of Trust Preferred Securities of PECO Trust III and IV, which are 100% owned finance subsidiaries of PECO.

[13] Letters of credit (non-debt)—ComEd maintains non-debt letters of credit to provide credit support for certain transactions as requested by third parties.

[14] Performance guarantees—Reflects full and unconditional guarantee of Trust Preferred Securities of ComEd Financing III which is a 100% owned finance subsidiary of ComEd.

[15] Letters of credit (non-debt)—Non-debt letters of credit maintained to provide credit support for certain transactions as requested by third parties.

[16] Performance guarantees—Guarantees issued to ensure performance under specific contracts.

[17] Energy marketing contract guarantees—Guarantees issued to ensure performance under energy commodity contracts. Amount includes approximately $1.2 billion of guarantees previously issued by Constellation on behalf of its Generation and NewEnergy business to allow it the flexibility needed to conduct business with counterparties without having to post other forms of collateral. The majority of these guarantees contain evergreen provisions that require the guarantee to remain in effect until cancelled. Generation’s estimated net exposure for obligations under commercial transactions covered by these guarantees is approximately $0.4 billion at December 31, 2014, which represents the total amount Generation could be required to fund based on December 31, 2014 market prices.

[18] Nuclear insurance premiums — Represents the maximum amount that Generation would be required to pay for retrospective premiums in the event of nuclear disaster at any domestic site, including CENG sites, under the Secondary Financial Protection pool as required under the Price-Anderson Act as well as the current aggregate annual retrospective premium obligation that could be imposed by NEIL. See the Nuclear Insurance section within this note for additional details on Generation’s nuclear insurance premiums.