Decrease in Fair Value Adjustment

No definition available.

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

- Definition

This element represents realized gains or losses that are reclassified to results of operations due to the settlement of all derivative contracts during the respective period.

+ References

No definition available.

+ Details

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

- Details

Name:	exc_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems
Namespace Prefix:	exc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	exc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetLiabilityGainLossAbstract
Namespace Prefix:	exc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value measurement with unobservable inputs reconciliation recurring basis asset liability gain loss change in collateral.

+ References

No definition available.

+ Details

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

- Definition

This element represents total gains or losses for the period (realized and unrealized), arising from assets and liabilities measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings.

+ References

No definition available.

+ Details

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

- Definition

This element represents total unrealized gains or losses for the period, arising from the change in fair value related to assets and liabilities measured at fair value on a recurring basis using unobservable inputs (Level 3), held as of the balance sheet date.

+ References

No definition available.

+ Details

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

- Definition

+ References

No definition available.

+ Details

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

- Definition

+ References

No definition available.

+ Details

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

- Definition

+ References

No definition available.

+ Details

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

- Definition

This element represents an asset or liability measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

No definition available.

+ Details

Name:	exc_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetLiabilityValue
Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates.

+ References

No definition available.

+ Details

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

- Details

Name:	exc_FootnotesToFairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationAbstract
Namespace Prefix:	exc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Increase in fair value adjustment related to purchase accounting as a result of the exchnage offer.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of transfers of financial instrument classified as a liability into level 3 of the fair value hierarchy.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationLiabilityTransfersIntoLevel3
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Description of where the gain (loss), arising from assets measured at fair value on a recurring basis using unobservable inputs (level 3), is to be recognized in earnings.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarningsDescription
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchasesSalesIssuancesSettlementsAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersOutOfLevel3
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Description of where the gains or losses, arising from liabilities measured at fair value on a recurring basis using unobservable inputs (Level 3), are included in earnings or the statement of financial position.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarningsDescription
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of settlements of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of transfers of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset) into level 3 of the fair value hierarchy.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(3)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19279-110258

+ Details

Name:	us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationTransfersIntoLevel3
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	dei_LegalEntityAxis=exc_ExelonGenerationCoLLCMember
Namespace Prefix:
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- Details

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Namespace Prefix:
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- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
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Fair Value of Financial Assets and Liabilities - Fair Value Assets Liabilities Measured On Recurring Basis Unobservable Input Reconciliation (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Sep. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2014
Derivative [Member] \| Consolidation, Eliminations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 0
Total realized / unrealized gains (losses)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates	(8)
Included in payable for Zion Station decommissioning	0
Included in noncurrent payables to affiliates	8
Change in collateral	0
Purchases, sales, issuances and settlements
Purchases	0
Sales	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0
Transfers into Level 3	0
Transfers out of Level 3	0
The amount of total losses included in income attributed to the change in unrealized gains (losses) related to assets and liabilities held	0
Exelon Generation Co L L C [Member]
Purchases, sales, issuances and settlements
Settlements	2		5
Footnotes To Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Abstract]
Gain (loss) reclassified to results of operating due to the settlement of derivative contracts	(134)	212
Decrease in Fair Value Adjustment	36
Increase In Fair Value Adjustment			30
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning balance	1,721		749
Total realized / unrealized gains (losses)
Included in net income	(30)		(311)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates	0		0
Included in payable for Zion Station decommissioning	(3)		1
Included in noncurrent payables to affiliates	(26)		28
Change in collateral	(12)		(144)
Purchases, sales, issuances and settlements
Purchases	93		181
Sales	(22)		(7)
Settlements	(29)		(6)
Transfers into Level 3	(4)		26
Transfers out of Level 3	(5)		1
Ending balance	1,721		752
The amount of total losses included in income attributed to the change in unrealized gains (losses) related to assets and liabilities held	181		(446)
Fair Value, Inputs, Level 3 [Member] \| Derivative [Member] \| Consolidation, Eliminations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	0		0	0
Total realized / unrealized gains (losses)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates			(3)
Included in payable for Zion Station decommissioning			0
Included in noncurrent payables to affiliates			3
Change in collateral			0
Purchases, sales, issuances and settlements
Purchases			0
Sales			0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements			0
Transfers into Level 3			0
Transfers out of Level 3			0
The amount of total losses included in income attributed to the change in unrealized gains (losses) related to assets and liabilities held			0
Fair Value, Inputs, Level 3 [Member] \| Exelon Generation Co L L C [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning balance	1,928		942
Total realized / unrealized gains (losses)
Included in net income	(30)		(311)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates	8		3
Included in payable for Zion Station decommissioning	(3)		1
Included in noncurrent payables to affiliates	0		0
Change in collateral	(12)		(144)
Purchases, sales, issuances and settlements
Purchases	93		181
Sales	(22)		(7)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(29)
Settlements			(6)
Transfers into Level 3	(4)		26
Transfers out of Level 3	(5)		1
Ending balance	1,962		920
The amount of total losses included in income attributed to the change in unrealized gains (losses) related to assets and liabilities held	181		(446)
Fair Value, Inputs, Level 3 [Member] \| Exelon Generation Co L L C [Member] \| Nuclear Decommissioning Trust Fund Investment Level Three Asset [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	2		1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	715		486	350	691
Total realized / unrealized gains (losses)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates	8		3
Included in payable for Zion Station decommissioning	0		0
Included in noncurrent payables to affiliates	0		0
Change in collateral	0		0
Purchases, sales, issuances and settlements
Purchases	47		139
Sales	(8)		(1)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(29)		(6)
Transfers into Level 3	(4)		0
Transfers out of Level 3	0		0
The amount of total losses included in income attributed to the change in unrealized gains (losses) related to assets and liabilities held	1		0
Fair Value, Inputs, Level 3 [Member] \| Exelon Generation Co L L C [Member] \| Pledged Assets For Zion Station Decommissioning [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	178		137	112	184
Total realized / unrealized gains (losses)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates	0		0
Included in payable for Zion Station decommissioning	(3)		1
Included in noncurrent payables to affiliates	0		0
Change in collateral	0		0
Purchases, sales, issuances and settlements
Purchases	5		30
Sales	(14)		(4)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0		0
Transfers into Level 3			0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3	0
Transfers out of Level 3	0		0
The amount of total losses included in income attributed to the change in unrealized gains (losses) related to assets and liabilities held	0		0
Fair Value, Inputs, Level 3 [Member] \| Exelon Generation Co L L C [Member] \| Derivative [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	1,066		287	465	1,050
Total realized / unrealized gains (losses)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings, Description	-32		-312
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates	0		0
Included in payable for Zion Station decommissioning	0		0
Included in noncurrent payables to affiliates	0
Change in collateral	(12)		(144)
Purchases, sales, issuances and settlements
Purchases	41		10
Sales	0		(2)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0		0
Transfers into Level 3			26
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3	0
Transfers out of Level 3	(5)		8
The amount of total losses included in income attributed to the change in unrealized gains (losses) related to assets and liabilities held	180		(446)
Fair Value, Inputs, Level 3 [Member] \| Exelon Generation Co L L C [Member] \| Other Investments [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	3		10	15	3
Total realized / unrealized gains (losses)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings, Description	0		0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates	0		0
Included in payable for Zion Station decommissioning	0		0
Included in noncurrent payables to affiliates	0		0
Change in collateral	0		0
Purchases, sales, issuances and settlements
Purchases	0		2
Sales	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0		0
Transfers into Level 3	0		0
Transfers out of Level 3	0		(7)
The amount of total losses included in income attributed to the change in unrealized gains (losses) related to assets and liabilities held			0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Liability Gain Loss Included In Earnings Attributed To Changes In Unrealized Gains Losses	0
Fair Value, Inputs, Level 3 [Member] \| Commonwealth Edison Co [Member] \| Derivative [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	(241)		(168)	(193)	(207)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	0		0
Total realized / unrealized gains (losses)
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Included In Noncurrent Payables To Affiliates	0		0
Included in payable for Zion Station decommissioning	0		0
Included in noncurrent payables to affiliates	(34)		25
Change in collateral	0		0
Purchases, sales, issuances and settlements
Purchases	0		0
Sales	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0		0
Transfers into Level 3	0		0
Transfers out of Level 3	0		0
The amount of total losses included in income attributed to the change in unrealized gains (losses) related to assets and liabilities held	$ 0		$ 0