Commitments and Contingencies - Energy Commitments (Details) $ in Millions		Jun. 30, 2015 USD ($)
Exelon Generation Co L L C [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total		$ 1,893
2015		283
2016		583
2017		410
2018		185
2019		130
Thereafter		302
Exelon Generation Co L L C [Member] | Net Capacity Purchases [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	[1]	1,165
2015	[1]	218
2016	[1]	280
2017	[1]	207
2018	[1]	96
2019	[1]	101
Thereafter	[1]	263
Exelon Generation Co L L C [Member] | Power Purchases [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	[2]	617
2015	[2]	58
2016	[2]	288
2017	[2]	187
2018	[2]	72
2019	[2]	11
Thereafter	[2]	1
Exelon Generation Co L L C [Member] | Transmission Rights Purchases [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	[3]	111
2015	[3]	7
2016	[3]	15
2017	[3]	16
2018	[3]	17
2019	[3]	18
Thereafter	[3]	38
Exelon Generation Co L L C [Member] | CapacityOffsets [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2015		75
2016		146
2017		149
2018		150
2019		151
Operating Leases, Future Minimum Payments Receivable [Abstract]
Thereafter		604
Commonwealth Edison Co [Member] | Energy Supply Procurement [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	[4]	697
2015	[4]	251
2016	[4]	262
2017	[4]	163
2018	[4]	21
2019	[4]	0
Thereafter	[4]	0
Commonwealth Edison Co [Member] | Renewable Energy Including Renewable Energy Credits [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	[5]	1,481
2015	[5]	38
2016	[5]	76
2017	[5]	77
2018	[5]	78
2019	[5]	79
Thereafter	[5]	1,133
PECO Energy Co [Member] | DSP Program Electric Procurement Contracts [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	[6]	671
2015	[6]	368
2016	[6]	270
2017	[6]	33
2018	[6]	0
2019	[6]	0
Thereafter	[6]	0
PECO Energy Co [Member] | Alternative Energy Credits [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	[7]	13
2015	[7]	2
2016	[7]	2
2017	[7]	2
2018	[7]	2
2019	[7]	2
Thereafter	[7]	3
Baltimore Gas and Electric Company [Member] | Energy Supply Procurement [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	[8]	1,389
2015	[8]	462
2016	[8]	675
2017	[8]	252
2018	[8]	0
2019	[8]	0
Thereafter	[8]	0
Baltimore Gas and Electric Company [Member] | Curtailment Services [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	[9]	95
2015	[9]	20
2016	[9]	34
2017	[9]	29
2018	[9]	12
2019	[9]	$ 0

[1] Net capacity purchases include PPAs and other capacity contracts including those that are accounted for as operating leases. Amounts presented in the commitments represent Generation’s expected payments under these arrangements at June 30, 2015, net of fixed capacity payments expected to be received ("capacity offsets") by Generation under contracts to resell such acquired capacity to third parties under long-term capacity sale contracts. As of June 30, 2015, capacity offsets were $75 million, $146 million, $149 million, $150 million, $151 million, and $604 million for years 2015, 2016, 2017, 2018, 2019, and thereafter, respectively. Expected payments include certain fixed capacity charges which may be reduced based on plant availability.

[2] The table excludes renewable energy purchases that are contingent in nature.

[3] Transmission rights purchases include estimated commitments for additional transmission rights that will be required to fulfill firm sales contracts.

[4] ComEd entered into various contracts for the procurement of electricity that started to expire in 2012, and will continue to expire through 2018. ComEd is permitted to recover its electric supply procurement costs from retail customers with no mark-up. As of June 30, 2015, ComEd has completed the ICC-approved procurement process for a portion of its energy requirements through the periods ending May 31, 2015, 2016 and 2017.

[5] Primarily related to ComEd 20-year contracts for renewable energy and RECs that began in June 2012. ComEd is permitted to recover its renewable energy and REC costs from retail customers with no mark-up. The commitments represent the maximum settlements with suppliers for renewable energy and RECs under the existing contract terms.

[6] PECO entered into various contracts for the procurement of electric supply to serve its default service customers that expire between 2015 and 2017. PECO is permitted to recover its electric supply procurement costs from default service customers with no mark-up in accordance with its PAPUC-approved DSP Programs. See Note 5 — Regulatory Matters for additional information.

[7] PECO is subject to requirements related to the use of alternative energy resources established by the AEPS Act. See Note 3 — Regulatory Matters of the Exelon 2014 Form 10-K for additional information.

[8] BGE entered into various contracts for the procurement of electricity that expire between 2015 through 2017. The cost of power under these contracts is recoverable under MDPSC approved fuel clauses. See Note 3 — Regulatory Matters of the Exelon 2014 10-K for additional information.

[9] BGE has entered into various contracts with curtailment services providers related to transactions in PJM’s capacity market. See Note 3 —Regulatory Matters of the Exelon 2014 Form 10-K for additional information.