Plant Retirements (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended	37 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012
Plant Retirements Costs [Abstract]
Inventory write down related to plant retirements	$ 6.00
Exelon Generation Co L L C [Member]
Plant Retirements Reserve [Line Items]
Severance benefit obligation - beginning balance	7.00	7.00
Severance charges recorded	0	4.00
Cash payments	(4.00)	(4.00)
Severance benefit obligation - ending balance	3.00	7.00	3.00
Plant Retirements Costs [Abstract]
Plant retirement costs incurred			44.00
Severance benefits expense related to plant retirements		4.00	13.00
Inventory write down related to plant retirements	6.00		18.00
Plant shut-down costs	11.00	2.00	13.00
Exelon Generation Co L L C [Member] \| Eddystone Generating Station [Member]
Plant Retirements Reliability Must Run Revenue [Abstract]
Monthly revenue during reliability-must-run period	6.00
Exelon Generation Co L L C [Member] \| Schuylkill Station Unit One [Member]
Plant Retirement Positions Eliminated [Abstract]
Oil/gas-fired generation unit to be retired	166		166
Exelon Generation Co L L C [Member] \| Riverside Station Unit Six [Member]
Plant Retirement Positions Eliminated [Abstract]
Oil/gas-fired generation unit to be retired	115		115
Commonwealth Edison Co [Member]
Plant Retirements Costs [Abstract]
Inventory write down related to plant retirements	$ 1.00

Represents number of oil/gas-fired generating units expected to be retired as part of the plant retirements.

No definition available.

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- Definition

Provides information regarding the terms and conditions under which Generation will continue to operate retired units for reliability purposes beyond their planned deactivation date, which is subject to FERC approval.

+ References

No definition available.

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- Definition

Cash payments under the severance benefit obligation related to plant retirement.

+ References

No definition available.

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- Definition

Represents the liability recorded for severance benefits obligations as of the balance sheet date related to plant retirements.

+ References

No definition available.

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- Definition

Amount charged against earnings in the period for a specified incurred and estimated severance cost associated with exit from or disposal of business activities or restructuring pursuant to a duly authorized plan.

+ References

No definition available.

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- Definition

The charge against earnings in the period for known and estimated costs of termination benefits provided to current employees that are involuntarily terminated under a benefit arrangement associated with plant retirements, excluding costs or losses pertaining to an entity newly acquired in a business combination or a discontinued operation as defined by generally accepted accounting principles and costs associated with one-time termination benefits.

+ References

No definition available.

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- Definition

The charge against earnings in the period, comprised of costs incurred associated with an exit or disposal activity other than for a discontinued operations as defined under generally accepted accounting principles. Costs of such activities include those for one-time termination benefits, termination of an operating lease or other contract, consolidating or closing facilities, and relocating employees, and costs associated with an ongoing benefit arrangement, but excludes costs associated with the retirement of a long-lived asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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Charge to cost of goods sold that represents the reduction of the carrying amount of inventory, generally attributable to obsolescence or market conditions.

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The charge against earnings in the period, comprised of costs associated with restructuring activities not otherwise specified in the taxonomy pursuant to a duly authorized plan, excluding a discontinued operation as defined by generally accepted accounting principles. Costs of such activities include those for one-time termination benefits, termination of an operating lease or other contract, consolidating or closing facilities, and relocating employees, but excludes costs associated with the retirement of a long-lived asset and severance costs associated with established compensation plans.

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