Commitments and Contingencies - Schedule of Purchases of Energy, Capacity and Transmission Rights (Details) (Exelon Generation Co L L C [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Capacity Offsets [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
2015	$ 132
2016	133	[1]
2017	136
2018	137
2019	138
Thereafter	591
Net Capacity Purchases [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
2015	418	[1]
2016	283	[1]
2017	222	[1]
2018	112	[1]
2019	117	[1]
Thereafter	279	[1]
Total	1,431	[1]
Power Purchases [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
2015	152	[2]
2016	228	[2]
2017	121	[2]
2018	29	[2]
2019	5	[2]
Thereafter	1	[2]
Total	536	[2]
Transmission Rights Purchases [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
2015	20	[3]
2016	15	[3]
2017	15	[3]
2018	16	[3]
2019	16	[3]
Thereafter	35	[3]
Total	117	[3]
Total Unregulated Energy Commitments [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
2015	590
2016	526
2017	358
2018	157
2019	138
Thereafter	315
Total	$ 2,084

[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 December 31, 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 December 31, 2014, capacity offsets were $132 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.

[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.