Commitments and Contingencies - Schedule of Commercial Commitments (Details) $ in Millions	Dec. 31, 2015 USD ($)
Guarantor Obligations [Line Items]
Total	$ 9,206
2015	5,424
2016	54
2017	3
2018	2
2019	29
2020 and beyond	$ 3,694
Percentage ownership of common stock	100.00%
Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Total	$ 1,583	[1]
2015	1,565	[1]
2016	5	[1]
2017	0	[1]
2018	0	[1]
2019	13	[1]
2020 and beyond	0	[1]
Surety Bond [Member]
Guarantor Obligations [Line Items]
Total	809	[2]
2015	733	[2]
2016	49	[2]
2017	3	[2]
2018	2	[2]
2019	16	[2]
2020 and beyond	6	[2]
Performance Guarantee [Member]
Guarantor Obligations [Line Items]
Total	628	[3]
2015	0	[2]
2016	0	[2]
2017	0	[2]
2018	0	[2]
2019	0	[2]
2020 and beyond	628	[2]
Energy Contract Guarantee [Member]
Guarantor Obligations [Line Items]
Total	3,126	[4]
2015	3,126	[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	3,100
Nuclear Insurance Premiums [Member]
Guarantor Obligations [Line Items]
Total	3,060	[5]
2015	0	[5]
2016	0	[5]
2017	0	[5]
2018	0	[5]
2019	0	[5]
2020 and beyond	3,060	[5]
Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]
Guarantor Obligations [Line Items]
Estimated net exposure for commercial transaction obligations	500
Baltimore Gas and Electric Company [Member]
Guarantor Obligations [Line Items]
Total	262
2015	12
2016	0
2017	0
2018	0
2019	0
2020 and beyond	250
Baltimore Gas and Electric Company [Member] | Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Total	2	[6]
2015	2	[6]
2016	0	[6]
2017	0	[6]
2018	0	[6]
2019	0	[6]
2020 and beyond	0	[6]
Baltimore Gas and Electric Company [Member] | Surety Bond [Member]
Guarantor Obligations [Line Items]
Total	10	[7]
2015	10	[7]
2016	0	[7]
2017	0	[7]
2018	0	[7]
2019	0	[7]
2020 and beyond	0	[7]
Baltimore Gas and Electric Company [Member] | Performance Guarantee [Member]
Guarantor Obligations [Line Items]
Total	250	[8]
2015	0	[8]
2016	0	[8]
2017	0	[8]
2018	0	[8]
2019	0	[8]
2020 and beyond	250	[8]
Baltimore Gas and Electric Company [Member] | Trust Preferred Securities [Member]
Guarantor Obligations [Line Items]
Total	250
PECO Energy Co [Member]
Guarantor Obligations [Line Items]
Total	209
2015	31
2016	0
2017	0
2018	0
2019	0
2020 and beyond	178
PECO Energy Co [Member] | Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Total	22	[9]
2015	22	[9]
2016	0	[9]
2017	0	[9]
2018	0	[9]
2019	0	[9]
2020 and beyond	0	[9]
PECO Energy Co [Member] | Surety Bond [Member]
Guarantor Obligations [Line Items]
Total	9	[10]
2015	9	[10]
2016	0	[10]
2017	0	[10]
2018	0	[10]
2019	0	[10]
2020 and beyond	0	[10]
PECO Energy Co [Member] | Performance Guarantee [Member]
Guarantor Obligations [Line Items]
Total	178	[11]
2015	0	[11]
2016	0	[11]
2017	0	[11]
2018	0	[11]
2019	0	[11]
2020 and beyond	178	[11]
PECO Energy Co [Member] | Trust Preferred Securities [Member]
Guarantor Obligations [Line Items]
Total	178
Commonwealth Edison Co [Member]
Guarantor Obligations [Line Items]
Total	224
2015	22
2016	0
2017	2
2018	0
2019	0
2020 and beyond	200
Commonwealth Edison Co [Member] | Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Total	16	[12]
2015	16	[12]
2016	0	[12]
2017	0	[12]
2018	0	[12]
2019	0	[12]
2020 and beyond	0	[12]
Commonwealth Edison Co [Member] | Surety Bond [Member]
Guarantor Obligations [Line Items]
Total	8	[13]
2015	6	[13]
2016	0	[13]
2017	2	[13]
2018	0	[13]
2019	0	[13]
2020 and beyond	0	[13]
Commonwealth Edison Co [Member] | Performance Guarantee [Member]
Guarantor Obligations [Line Items]
Total	200	[14]
2015	0	[14]
2016	0	[14]
2017	0	[14]
2018	0	[14]
2019	0	[14]
2020 and beyond	200	[14]
Commonwealth Edison Co [Member] | Trust Preferred Securities [Member]
Guarantor Obligations [Line Items]
Total	200
Exelon Generation Co L L C [Member]
Guarantor Obligations [Line Items]
Total	6,832
2015	3,709
2016	50
2017	0
2018	0
2019	13
2020 and beyond	3,060
Exelon Generation Co L L C [Member] | Financial Standby Letter of Credit [Member]
Guarantor Obligations [Line Items]
Total	1,503	[15]
2015	1,485	[15]
2016	5	[15]
2017	0	[15]
2018	0	[15]
2019	13	[15]
2020 and beyond	0	[15]
Exelon Generation Co L L C [Member] | Surety Bond [Member]
Guarantor Obligations [Line Items]
Total	737
2015	692
2016	45
2017	0
2018	0
2019	0
2020 and beyond	0
Exelon Generation Co L L C [Member] | Energy Contract Guarantee [Member]
Guarantor Obligations [Line Items]
Total	1,532
2015	1,532	[16]
2016	0	[16]
2017	0	[16]
2018	0	[16]
2019	0	[16]
2020 and beyond	0	[16]
Estimated total assumed for commercial transaction obligations	1,500
Exelon Generation Co L L C [Member] | Nuclear Insurance Premiums [Member]
Guarantor Obligations [Line Items]
Total	3,060	[17]
2015	0	[17]
2016	0	[17]
2017	0	[17]
2018	0	[17]
2019	0	[17]
2020 and beyond	3,060	[17]
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	$ 300
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] ncludes $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 $3.1 billion of guarantees issued by Exelon and Generation on behalf of its Constellation businesses 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 $0.5 billion at December 31, 2015, which represents the total amount Exelon could be required to fund based on December 31, 2015 market prices.

[5] 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.

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

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

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

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

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

[11] 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.

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

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

[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] Energy marketing contract guarantees—Guarantees issued to ensure performance under energy commodity contracts. Amount includes approximately $1.5 billion of guarantees issued by Generation on behalf of its Constellation businesses 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 $0.3 billion at December 31, 2015, which represents the total amount Generation could be required to fund based on December 31, 2015 market prices.

[17] 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.