Commitments and Contingencies - Energy Commitments (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014
Other Purchase Obligations [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	$ 917
2014	103
2015	324
2016	180
2017	151
2018	36
Thereafter	123
Exelon Generation Co L L C [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	2,008
2014	104
2015	578
2016	450
2017	303
2018	129
Thereafter	444
Operating Leases, Future Minimum Payments Receivable [Abstract]
2014	23
2015	132
2016	133
2017	136
2018	137
Thereafter	729
Exelon Generation Co L L C [Member] | Other Purchase Obligations [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	493	[1],[2]
2014	80	[1],[2]
2015	182	[1],[2]
2016	57	[1],[2]
2017	43	[1],[2]
2018	30	[1],[2]
Thereafter	101	[1],[2]
Exelon Generation Co L L C [Member] | Net Capacity Purchases [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	1,451	[3]
2014	91	[3]
2015	396	[3]
2016	269	[3]
2017	208	[3]
2018	98	[3]
Thereafter	389	[3]
Exelon Generation Co L L C [Member] | Power Purchases [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	434	[4]
2014	7	[4]
2015	162	[4]
2016	166	[4]
2017	80	[4]
2018	15	[4]
Thereafter	4	[4]
Exelon Generation Co L L C [Member] | Transmission Rights Purchases [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	123	[5]
2014	6	[5]
2015	20	[5]
2016	15	[5]
2017	15	[5]
2018	16	[5]
Thereafter	51	[5]
Commonwealth Edison Co [Member] | Other Purchase Obligations [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	92	[6]
2014	13	[6]
2015	38	[6]
2016	16	[6]
2017	5	[6]
2018	5	[6]
Thereafter	15	[6]
Commonwealth Edison Co [Member] | Energy Supply Procurement [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	731	[7]
2014	111	[7]
2015	329	[7]
2016	151	[7]
2017	140	[7]
2018	0	[7]
Thereafter	0	[7]
Commonwealth Edison Co [Member] | Renewable Energy Including Renewable Energy Credits [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	1,538	[8]
2014	22	[8]
2015	73	[8]
2016	76	[8]
2017	77	[8]
2018	78	[8]
Thereafter	1,212	[8]
PECO Energy Co [Member] | Other Purchase Obligations [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	29	[6]
2014	7	[6]
2015	11	[6]
2016	2	[6]
2017	1	[6]
2018	1	[6]
Thereafter	7	[6]
PECO Energy Co [Member] | DSP Program Electric Procurement Contracts [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	498	[9]
2014	193	[9]
2015	305	[9]
2016	0	[9]
2017	0	[9]
2018	0	[9]
Thereafter	0	[9]
PECO Energy Co [Member] | Alternative Energy Credits [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	13	[10]
2014	1	[10]
2015	2	[10]
2016	2	[10]
2017	2	[10]
2018	2	[10]
Thereafter	4	[10]
Baltimore Gas and Electric Company [Member] | Other Purchase Obligations [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	302	[6]
2014	2	[6]
2015	93	[6]
2016	105	[6]
2017	102	[6]
2018	0	[6]
Thereafter	0	[6]
Baltimore Gas and Electric Company [Member] | Energy Supply Procurement [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	1,055	[11]
2014	198	[11]
2015	621	[11]
2016	236	[11]
2017	0	[11]
2018	0	[11]
Thereafter	0	[11]
Baltimore Gas and Electric Company [Member] | Curtailment Services [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total	125	[12]
2014	10	[12]
2015	40	[12]
2016	34	[12]
2017	29	[12]
2018	$ 12	[12]

[1] Purchase obligations do not include commitments related to construction contracts. See Construction Commitments section below for additional information.

[2] Purchase obligations include commitments related to assets-held-for-sale. See Note 4 - Mergers, Acquisitions and Dispositions for additional information.

[3] 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 September 30, 2014, 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 September 30, 2014, capacity offsets were $23 million, $132, million $133 million, $136, million, $137 million, and $729 million for years 2014, 2015, 2016, 2017, 2018, and thereafter, respectively. Expected payments include certain fixed capacity charges which may be reduced based on plant availability.

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

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

[6] Purchase obligations include commitments related to smart meter installation. See Note 5 — Regulatory Matters for additional information.

[7] ComEd entered into various contracts for the procurement of electricity that started to expire in 2012, and will continue to expire through 2017. ComEd is permitted to recover its electric supply procurement costs from retail customers with no mark-up. As of September 30, 2014, 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.

[8] 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.

[9] PECO entered into various contracts for the procurement of electric supply to serve its default service customers that expire between 2014 and 2015. 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.

[10] PECO is subject to requirements related to the use of alternative energy resources established by the AEPS Act. See Note 5 — Regulatory Matters for additional information.

[11] BGE entered into various contracts for the procurement of electricity that expire between 2014 through 2016. The cost of power under these contracts is recoverable under MDPSC approved fuel clauses. See Note 5 — Regulatory Matters for additional information.

[12] BGE has entered into various contracts with curtailment services providers related to transactions in PJM’s capacity market. See Note 5 —Regulatory Matters for additional information.