Commitments and Contingencies - Energy Commitments (Details) (USD $) In Millions, unless otherwise specified	Apr. 01, 2015		Mar. 31, 2015
Other Purchase Obligations [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total			$ 840
2014			258
2015			279
2016			152
2017			38
2018			30
Thereafter			83
Energy Supply Procurement [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2014	179	[1]
2015	112	[1]
CapacityOffsets [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2014			107
2015			133
2016	23		136
2017	21		137
2018			138
Operating Leases, Future Minimum Payments Receivable [Abstract]
Thereafter			591
Exelon Generation Co L L C [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total			2,028
2014			454
2015			560
2016			387
2017			177
2018			138
Thereafter			312
Exelon Generation Co L L C [Member] | Other Purchase Obligations [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total			364	[2],[3]
2014			123	[2],[3]
2015			81	[2],[3]
2016			43	[2],[3]
2017			31	[2],[3]
2018			23	[2],[3]
Thereafter			63	[2],[3]
Exelon Generation Co L L C [Member] | Net Capacity Purchases [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total			1,321	[4]
2014			317	[4]
2015			287	[4]
2016			219	[4]
2017			109	[4]
2018			113	[4]
Thereafter			276	[4]
Exelon Generation Co L L C [Member] | Power Purchases [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total			597	[5]
2014			124	[5]
2015			258	[5]
2016			153	[5]
2017			52	[5]
2018			9	[5]
Thereafter			1	[5]
Exelon Generation Co L L C [Member] | Transmission Rights Purchases [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total			110	[6]
2014			13	[6]
2015			15	[6]
2016			15	[6]
2017			16	[6]
2018			16	[6]
Thereafter			35	[6]
Commonwealth Edison Co [Member] | Other Purchase Obligations [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total			152	[7]
2014			53	[7]
2015			82	[7]
2016			2	[7]
2017			2	[7]
2018			2	[7]
Thereafter			11	[7]
Commonwealth Edison Co [Member] | Energy Supply Procurement [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total			473	[1]
2014			182	[1]
2015			151	[1]
2016			140	[1]
2017			0	[1]
2018			0	[1]
Thereafter			0	[1]
Commonwealth Edison Co [Member] | Renewable Energy Including Renewable Energy Credits [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total			1,498	[8]
2014			56	[8]
2015			76	[8]
2016			77	[8]
2017			78	[8]
2018			84	[8]
Thereafter			1,127	[8]
PECO Energy Co [Member] | Other Purchase Obligations [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total			11	[7]
2014			5	[7]
2015			6	[7]
2016			0	[7]
2017			0	[7]
2018			0	[7]
Thereafter			0	[7]
PECO Energy Co [Member] | DSP Program Electric Procurement Contracts [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total			832	[9]
2014			532	[9]
2015			268	[9]
2016			32	[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			2	[10]
2015			2	[10]
2016			2	[10]
2017			2	[10]
2018			2	[10]
Thereafter			3	[10]
Baltimore Gas and Electric Company [Member] | Other Purchase Obligations [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total			313	[7]
2014			77	[7]
2015			110	[7]
2016			107	[7]
2017			5	[7]
2018			5	[7]
Thereafter			9	[7]
Baltimore Gas and Electric Company [Member] | Energy Supply Procurement [Member]
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
Total			1,074	[11]
2014			538	[11]
2015			448	[11]
2016			88	[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			105	[12]
2014			30	[12]
2015			34	[12]
2016			29	[12]
2017			12	[12]
2018			$ 0	[12]

[1] 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 March 31, 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.

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

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[4] 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 March 31, 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 March 31, 2015, capacity offsets were $107 million, $133 million, $136 million, $137, million, $138 million, and $591 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.

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

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

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

[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 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.

[10] 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.

[11] 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.

[12] 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.