Commitments and Contingencies - Narrative (Details)		1 Months Ended			3 Months Ended	12 Months Ended
		Jan. 31, 2013 USD ($)	Oct. 31, 2007 USD ($)	May. 31, 2006 Principle_responsible_party	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) a MGPSite reactor claimant Open_claim Customer	Dec. 31, 2014 USD ($)	Dec. 31, 1999 Principle_responsible_party	May. 30, 2012 USD ($)	Dec. 31, 2003
Commitments and Contingencies [Line Items]
Nuclear insurance liability limit per incident						$ 18,300,000.0
Cost surcharge to Price-Anderson Act nuclear incident assessment						5.00%
Guarantee obligations maximum exposure						$ 9,206,000,000
Asbestos liability reserve						95,000,000	$ 100,000,000
Probable contingency (liability)						$ 21,000,000
Open asbestos liability claims | Open_claim						228
Asbestos liability reserve related to anticipated claims						$ 74,000,000
Rossville ash site [Member]
Commitments and Contingencies [Line Items]
Area of property | a						32
Nuclear Insurance Premiums [Member]
Commitments and Contingencies [Line Items]
Guarantee obligations maximum exposure	[1]					$ 3,060,000,000
Exelon Generation Co L L C [Member]
Commitments and Contingencies [Line Items]
Nuclear financial protection pool value						$ 375,000,000
United States licensed nuclear reactors total | reactor						103
Maximum recovery limit from a nuclear industry mutual insurance company in the event of multiple losses						$ 13,100,000,000.0
Cost surcharge to Price-Anderson Act nuclear incident assessment						12730000000.00%
Maximum assessment mandated by Price-Anderson Act per nuclear reactor for a nuclear incident						$ 19,000,000
Maximum annual assessment payment mandated by Price-Anderson Act for a nuclear incident						2,700,000,000
Total retrospective premium obligation under insurance from a nuclear industry mutual insurance company						365,000,000
Mutual Replacement Power Cost Insurance Maximum Retrospective Premium Obligation						3,200,000,000
Cost of spent nuclear fuel disposal per kWh of net nuclear generation						0.001
Net nuclear fuel disposal fees						136,000,000	49,000,000
Department of Energy SNF one-time fee applicable to nuclear generation						277,000,000
DOE SNF one-time fee with interest						$ 1,021,000,000
13-week Treasury Rate used to calculate DOE SNF one-time fee						0.112%
Guarantee obligations maximum exposure						$ 6,832,000,000
Consent decree penalty			$ 1,000,000
Environmental loss contingencies						$ 12,000,000	$ 13,000,000
Payments for operating leases		$ 14,000,000
Open asbestos liability claims | Open_claim						300
Exelon Generation Co L L C [Member] | Cotter Corporation [Member]
Commitments and Contingencies [Line Items]
Total cost of remediation to be shared by PRPs						$ 60,000,000
DOJ potential settlement						90,000,000
Exelon Generation Co L L C [Member] | Rossville ash site [Member]
Commitments and Contingencies [Line Items]
Estimate of possible loss						9,000,000
Exelon Generation Co L L C [Member] | Equity Method Investments [Member]
Commitments and Contingencies [Line Items]
Purchase obligations, due within two years						21,000,000
Unrecorded Unconditional Purchase Obligation, Due within Three Years						7,000,000
Unrecorded Unconditional Purchase Obligation, Due within Four Years						0
Unrecorded Unconditional Purchase Obligation						327,000,000
Unrecorded unconditional purchase obligation, due in next 12 months						299,000,000
Other unrecorded amounts						20,000,000
Exelon Generation Co L L C [Member] | Nuclear Insurance Premiums [Member]
Commitments and Contingencies [Line Items]
Nuclear insurance liability limit per incident						13,500,000,000.0
Guarantee obligations maximum exposure	[2]					3,060,000,000
Exelon Generation Co L L C [Member] | Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]
Commitments and Contingencies [Line Items]
Mutual Property Insurance Distribution To Members						18,500,000
Midwest Generation, LLC [Member]
Commitments and Contingencies [Line Items]
Percentage agreed to reimburse related parties										50.00%
Commonwealth Edison Co [Member]
Commitments and Contingencies [Line Items]
Guarantee obligations maximum exposure						$ 224,000,000
Total number of MGP sites | MGPSite						42
Sites approved for clean-up | MGPSite						17
Sites under study/remediation | MGPSite						25
Minimum number of customers ComEd can be held liable to for power interruption | Customer						30,000
Commonwealth Edison Co [Member] | Accrual For MGP Investigation And Remediation [Member]
Commitments and Contingencies [Line Items]
Increase (decrease) in accrual for environmental loss contingencies					$ 50,000,000
PECO Energy Co [Member]
Commitments and Contingencies [Line Items]
Guarantee obligations maximum exposure						$ 209,000,000
Total number of MGP sites | MGPSite						26
Sites approved for clean-up | MGPSite						16
Sites under study/remediation | MGPSite						10
Baltimore Gas and Electric Company [Member]
Commitments and Contingencies [Line Items]
Guarantee obligations maximum exposure						$ 262,000,000
Total number of MGP sites | MGPSite						13
Sites under study/remediation | MGPSite						2
Maximum estimated clean-up costs for all potentially responsible parties									$ 1,700,000.0
Number of claimants | claimant						454
Baltimore Gas and Electric Company [Member] | Deferrable Interest Subordinated Debentures [Member]
Commitments and Contingencies [Line Items]
Interest rate on long-term debt						6.20%
Baltimore Gas and Electric Company [Member] | Accrual For MGP Investigation And Remediation [Member]
Commitments and Contingencies [Line Items]
Increase (decrease) in accrual for environmental loss contingencies					$ 1,000,000
Baltimore Gas and Electric Company [Member] | Sixty-Eighth Street Dump [Member]
Commitments and Contingencies [Line Items]
Number of parties jointly and severally liable In environmental protection agency action | Principle_responsible_party				19				19
Minimum estimated clean-up costs for all potentially responsible parties						$ 50,000,000
Maximum estimated clean-up costs for all potentially responsible parties						$ 64,000,000

[1] 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.

[2] 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.