Fair Value of Financial Assets and Liabilities - Fair Value Inputs Assets Quantitative Information (Details) - Fair Value, Inputs, Level 3 [Member]	12 Months Ended
Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Cash Collateral Posted	$ (34,000,000)	$ 162,000,000
Economic Hedges [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative assets, fair value	$ (66,000,000)	$ 245,000,000
Economic Hedges [Member] \| Minimum [Member] \| Discounted Cash Flow [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Forward power price assets	8.86	2.25
Forward gas price assets	1.69	1.57
Economic Hedges [Member] \| Minimum [Member] \| Option Model Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	0.24	0.11
Economic Hedges [Member] \| Maximum [Member] \| Discounted Cash Flow [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Forward power price assets	481	163
Forward gas price assets	17	7.88
Economic Hedges [Member] \| Maximum [Member] \| Option Model Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	2.84	2.37
Economic Hedges [Member] \| Arithmetic Average [Member] \| Discounted Cash Flow [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Forward power price assets	55	30
Forward gas price assets	3.50	2.59
Economic Hedges [Member] \| Arithmetic Average [Member] \| Option Model Valuation Technique [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	0.56	0.32
Derivative [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	$ (219,000,000)	$ (301,000,000)
Derivative [Member] \| Minimum [Member] \| Discounted Cash Flow [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	0.03	0.03
Fair Value Inputs Forward Heat Rate	900.00%	800.00%
Renewable factor	92.00%	91.00%
Derivative [Member] \| Maximum [Member] \| Discounted Cash Flow [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	0.07	0.08
Fair Value Inputs Forward Heat Rate	1000.00%	900.00%
Renewable factor	120.00%	123.00%
Derivative [Member] \| Arithmetic Average [Member] \| Discounted Cash Flow [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	0.0477	0.0493
Fair Value Inputs Forward Heat Rate	913.00%	885.00%
Renewable factor	97.00%	99.00%
Commonwealth Edison Co [Member] \| Derivative [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	$ (219,000,000)	$ (301,000,000)
Commonwealth Edison Co [Member] \| Derivative [Member] \| Minimum [Member] \| Discounted Cash Flow [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	0.03	0.03
Fair Value Inputs Forward Heat Rate	900.00%	800.00%
Renewable factor	92.00%	91.00%
Commonwealth Edison Co [Member] \| Derivative [Member] \| Maximum [Member] \| Discounted Cash Flow [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	0.07	0.08
Fair Value Inputs Forward Heat Rate	1000.00%	900.00%
Renewable factor	120.00%	123.00%
Commonwealth Edison Co [Member] \| Derivative [Member] \| Arithmetic Average [Member] \| Discounted Cash Flow [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Derivative Asset (Liability) Net, Measurement Input	0.0477	0.0493
Fair Value Inputs Forward Heat Rate	913.00%	885.00%
Renewable factor	97.00%	99.00%

Cash collateral posted related to credit risk.

No definition available.

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

- Definition

This element represents the forward power market price used to calculate the change in fair value of the derivative instrument.

+ References

No definition available.

+ Details

Name:	exc_FairValueInputsForwardGasPriceAssets
Namespace Prefix:	exc_
Data Type:	srt-types:perUnitItemType
Balance Type:	na
Period Type:	instant

- Definition

This element represents the factor that is multiplied with the forward price of natural gas to calculate a forward power curve. Natural gas has greater liquidity tenor than power and is commonly used to calculate this curve.

+ References

No definition available.

+ Details

Name:	exc_FairValueInputsForwardHeatRate
Namespace Prefix:	exc_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents the forward power market price used to calculate the change in fair value of the derivative instrument.

+ References

No definition available.

+ Details

Name:	exc_FairValueInputsForwardPowerPriceAssets
Namespace Prefix:	exc_
Data Type:	srt-types:perUnitItemType
Balance Type:	na
Period Type:	instant

- Definition

This element represents a factor to adjust an around the clock forward power price and quantity to be in line with an applicable renewable facility. Solar units generally produce more power in the summer days and wind units generally produce more power in the spring and fall evenings.

+ References

No definition available.

+ Details

Name:	exc_FairValueInputsRenewableFactor
Namespace Prefix:	exc_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Value of input used to measure net derivative asset (liability).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

+ Details

Name:	us-gaap_DerivativeAssetLiabilityNetMeasurementInput
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair value, after offset of derivative liability, of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, before offset against an obligation to return collateral under a master netting arrangement. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226006-175313

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=125515794&loc=d3e41678-113959

+ Details

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

- Definition

Fair value, after offset of derivative asset, of financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, elected not to be and before offset against a right to receive collateral under a master netting arrangement. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=125515794&loc=d3e41678-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226006-175313

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=exc_EconomicHedgesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ValuationTechniqueAxis=us-gaap_IncomeApproachValuationTechniqueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ValuationTechniqueAxis=exc_OptionModelValuationTechniqueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_ArithmeticAverageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_DerivativeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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