Common Stock - Components of Tax Benefits from Stock-based Compensation (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Common Stock [Abstract]
Stock options	$ 0	$ 0	$ 3
Restricted stock units	17	11	11
Performance share awards	11	11	7
Stock deferral plan	0exc_TaxBenefitFromStockDeferralPlan	1exc_TaxBenefitFromStockDeferralPlan	0exc_TaxBenefitFromStockDeferralPlan
Stock options	$ 0	$ 0	$ 2

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Excess tax benefits included in other financing activities of Exelon's Consolidated Statements of Cash Flows.

+ References

No definition available.

+ Details

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Balance Type:	debit
Period Type:	duration

- Definition

Reductions in the entity's income taxes that arise when compensation cost (from non-qualified performance share awards) recognized on the entity's tax return exceeds compensation cost from non-qualified performance share awards recognized on the income statement. This element increases net cash provided by operating activities.

+ References

No definition available.

+ Details

Name:	exc_TaxBenefitFromPerformanceShareAwardsDistributed
Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Reductions in the entity's income taxes that arise when compensation cost (from non-qualified restricted stock units) recognized on the entity's tax return exceeds compensation cost from non-qualified restricted stock units recognized on the income statement. This element increases net cash provided by operating activities.

+ References

No definition available.

+ Details

Name:	exc_TaxBenefitFromRestrictedStockUnitsDistributed
Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Reductions in the entity's income taxes that arise when compensation cost (from non-qualified stock deferral plans) recognized on the entity's tax return exceeds compensation cost from non-qualified stock deferral plans recognized on the income statement. This element increases net cash provided by operating activities.

+ References

No definition available.

+ Details

Name:	exc_TaxBenefitFromStockDeferralPlan
Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of deferred tax expense from write-off of the deferred tax asset related to deductible stock options at exercise.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 20

-Section 55

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=32706628&loc=d3e11283-113907

+ Details

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Period Type:	duration