Income Taxes - Reconciliation to Effective Tax Rate (Details)	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	35.00%	35.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	2.60%	(57.60%)
Qualified nuclear decommissioning trust fund income	1.90%	44.20%
Domestic production activities deduction	(2.20%)	(27.80%)
Health care reform legislation	0.00%	1.30%
Amortization of investment tax credit, net deferred taxes	(0.90%)	(18.00%)
Plant basis differences	(1.30%)	(31.40%)
Production tax credits and other credits	1.80%	36.50%
Noncontrolling interest	(0.70%)
Other	0.40%	(47.70%)
Effective income tax rate	33.00%	(138.50%)
Exelon Generation Co L L C [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	35.00%	35.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	2.70%	9.70%
Qualified nuclear decommissioning trust fund income	3.00%	(4.60%)
Domestic production activities deduction	(3.40%)	2.90%
Health care reform legislation	0.00%	0.00%
Amortization of investment tax credit, net deferred taxes	(1.40%)	1.70%
Plant basis differences	0.00%	0.00%
Production tax credits and other credits	2.80%	(3.80%)
Noncontrolling interest	(1.10%)
Other	(0.20%)	3.30%
Effective income tax rate	31.80%	51.80%
Commonwealth Edison Co [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	35.00%	35.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	5.00%	5.50%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%
Domestic production activities deduction	0.00%
Health care reform legislation	0.00%	0.10%
Amortization of investment tax credit, net deferred taxes	(0.30%)	(0.30%)
Plant basis differences	(0.30%)	(0.60%)
Production tax credits and other credits	0.00%	0.00%
Noncontrolling interest	0.00%
Other	0.20%	0.20%
Effective income tax rate	39.60%	39.90%
PECO Energy Co [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	35.00%	35.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	1.20%	1.20%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%
Domestic production activities deduction	0.00%
Health care reform legislation	0.00%	0.00%
Amortization of investment tax credit, net deferred taxes	(0.10%)	(0.10%)
Plant basis differences	(6.70%)	(8.70%)
Production tax credits and other credits	0.00%	0.00%
Noncontrolling interest	0.00%
Other	0.00%	0.20%
Effective income tax rate	29.40%	27.60%
Baltimore Gas and Electric Company [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
U.S. Federal statutory rate	35.00%	35.00%
Increase (decrease) due to:
State income taxes, net of Federal income tax benefit	5.30%	5.20%
Qualified nuclear decommissioning trust fund income	0.00%	0.00%
Domestic production activities deduction	0.00%
Health care reform legislation	0.20%	0.20%
Amortization of investment tax credit, net deferred taxes	0.00%	(0.20%)
Plant basis differences	(0.30%)	(0.60%)
Production tax credits and other credits	0.00%	0.00%
Noncontrolling interest	0.00%
Other	0.20%	0.10%
Effective income tax rate	40.40%	39.70%

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

The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate attributable to the elimination of the deduction previously received for Medicare prescription drug benefits in accordance with the Patient Protection and Affordable Care Act, as modified by the Health Care and Education Reconciliation Act.

+ References

No definition available.

+ Details

Name:	exc_EffectiveIncomeTaxRateReconciliationEliminationOfDeductionsMedicarePrescriptionDrugBenefit
Namespace Prefix:	exc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate that can be explained by the difference in depreciation and amortization methods allowed under generally accepted accounting principles and enacted tax laws.

+ References

No definition available.

+ Details

Name:	exc_EffectiveIncomeTaxRateReconciliationPlantBasisDifferences
Namespace Prefix:	exc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate that can be explained by income or losses generated by the qualified nuclear decommissioning trust funds that are taxed at a higher rate.

+ References

No definition available.

+ Details

Name:	exc_EffectiveIncomeTaxRateReconciliationQualifiedNuclearDecommissioningTrustFundIncomeLosses
Namespace Prefix:	exc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 13

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(h)(2))

-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

Name:	us-gaap_EffectiveIncomeTaxRateContinuingOperations
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Definition

Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 13

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 6.I)

-URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817

+ Details

Name:	us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to other deductions.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 13

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 6.I)

-URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817

+ Details

Name:	us-gaap_EffectiveIncomeTaxRateReconciliationDeductionsOther
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 13

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 6.I)

-URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817

+ Details

Name:	us-gaap_EffectiveIncomeTaxRateReconciliationDeductionsQualifiedProductionActivities
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 13

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 6.I)

-URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817

+ Details

Name:	us-gaap_EffectiveIncomeTaxRateReconciliationMinorityInterestIncomeExpense
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 13

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 6.I)

-URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817

+ Details

Name:	us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 13

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 6.I)

-URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817

+ Details

Name:	us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 13

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 6.I)

-URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817

+ Details

Name:	us-gaap_EffectiveIncomeTaxRateReconciliationTaxCreditsInvestment
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	dei_LegalEntityAxis=exc_BaltimoreGasAndElectricCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=exc_CommonwealthEdisonCoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=exc_ExelonGenerationCoLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=exc_PecoEnergyCoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: