Derivative Financial Instruments - Summary of Credit Risk Exposure (Details) - Exelon Generation Co L L C [Member] $ in Millions	9 Months Ended
Sep. 30, 2021 USD ($)
Derivative [Line Items]
Cash Collateral Held	$ 188
Letters Of Credit Held	117
Total Exposure Before Credit Collateral [Member]
Derivative [Line Items]
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	1,143
Total Exposure Before Credit Collateral [Member] \| Internal Investment Grade
Derivative [Line Items]
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	110
Total Exposure Before Credit Collateral [Member] \| Internal Noninvestment Grade
Derivative [Line Items]
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	309
Total Exposure Before Credit Collateral [Member] \| External Credit Rating, Investment Grade
Derivative [Line Items]
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	701
Total Exposure Before Credit Collateral [Member] \| External Credit Rating, Non Investment Grade
Derivative [Line Items]
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	23
Credit Collateral [Member]
Derivative [Line Items]
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	305
Credit Collateral [Member] \| Internal Investment Grade
Derivative [Line Items]
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	1
Credit Collateral [Member] \| Internal Noninvestment Grade
Derivative [Line Items]
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	48
Credit Collateral [Member] \| External Credit Rating, Investment Grade
Derivative [Line Items]
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	254
Credit Collateral [Member] \| External Credit Rating, Non Investment Grade
Derivative [Line Items]
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	2
Net Exposure [Member]
Derivative [Line Items]
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	838
Net Exposure [Member] \| Financial institutions [Member]
Derivative [Line Items]
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	53
Net Exposure [Member] \| Investor-owned utilities, marketers, power producers [Member]
Derivative [Line Items]
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	652
Net Exposure [Member] \| Energy cooperatives and municipalities [Member]
Derivative [Line Items]
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	62
Net Exposure [Member] \| Other [Member]
Derivative [Line Items]
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	71
Net Exposure [Member] \| Internal Investment Grade
Derivative [Line Items]
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	109
Net Exposure [Member] \| Internal Noninvestment Grade
Derivative [Line Items]
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	261
Net Exposure [Member] \| External Credit Rating, Investment Grade
Derivative [Line Items]
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	447
Net Exposure [Member] \| External Credit Rating, Non Investment Grade
Derivative [Line Items]
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	$ 21
Number Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Number of Counterparties	0
Number Of Counterparties Greater Than Ten Percent Of Net Exposure [Member] \| External Credit Rating, Investment Grade
Derivative [Line Items]
Number of Counterparties	0
Net Exposure Of Counterparties Greater Than Ten Percent Of Net Exposure [Member]
Derivative [Line Items]
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	$ 0
Net Exposure Of Counterparties Greater Than Ten Percent Of Net Exposure [Member] \| External Credit Rating, Investment Grade
Derivative [Line Items]
Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure	$ 0

Letters of credit held related to credit risk

No definition available.

Name:	exc_LettersOfCreditHeld
Namespace Prefix:	exc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents number of counterparties with a concentrated credit risk greater than 10% of net exposure.

+ References

No definition available.

+ Details

Name:	exc_NumberOfCounterparties
Namespace Prefix:	exc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date of cash collateral held for borrowed securities, for which the cash is restricted as to withdrawal or usage.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.1)
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.(a),2)
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	debit
Period Type:	instant

- Definition

Maximum amount of loss due to credit risk that, based on the gross fair value of the financial instrument, the entity would incur if parties to the financial instruments that make up the concentration failed completely to perform according to the terms of the contracts and the collateral or other security, if any, for the amount due proved to be of no value to the entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123594938&loc=d3e13537-108611

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- 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.

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