Debt and Credit Agreements - Narrative (Details) $ in Millions	6 Months Ended
Jun. 30, 2021 USD ($)
ShortTermDebt03232017 \| Corporate [Member]
Debt Instrument [Line Items]
Short-term Bank Loans and Notes Payable	$ 500
ShortTermDebt03242021 \| Corporate [Member]
Debt Instrument [Line Items]
Short-term Bank Loans and Notes Payable	200
ShortTermDebt03312021.1 \| Corporate [Member]
Debt Instrument [Line Items]
Short-term Bank Loans and Notes Payable	150
ShortTermDebt03312021.2 \| Corporate [Member]
Debt Instrument [Line Items]
Short-term Bank Loans and Notes Payable	150
ShortTermDebt03192020 \| Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Short-term Bank Loans and Notes Payable	200
ShortTermDebt300 \| Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Short-term Bank Loans and Notes Payable	300
ShortTermDebt01252021.1 \| Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Short-term Bank Loans and Notes Payable	125
ShortTermDebt01252021.2 \| Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Short-term Bank Loans and Notes Payable	125
ExGenBilatJan2013 \| Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	100
ExGenBilatFeb2019 \| Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	100
ExGenBilatJan2016 \| Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	150
WestMedMarch2026 \| Non-Recourse Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	150
Non-Recourse Debt	150
WestMedMarch2026 \| Non-Recourse Debt [Member] \| Interest Rate Swap [Member]
Debt Instrument [Line Items]
Derivative, Notional Amount	$ 113
Derivative, Fixed Interest Rate	0.61%
WestMedMarch2026 \| Exelon Generation Co L L C [Member] \| Non-Recourse Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms	LIBOR + 3
Debt Instrument, Face Amount	$ 150
Non-Recourse Debt	150
WestMedMarch2026 \| Exelon Generation Co L L C [Member] \| Non-Recourse Debt [Member] \| Interest Rate Swap [Member]
Debt Instrument [Line Items]
Derivative, Notional Amount	$ 113
Derivative, Fixed Interest Rate	0.61%
London Interbank Offered Rate (LIBOR) [Member] \| ShortTermDebt03232017 \| Corporate [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms	LIBOR plus 0.65
London Interbank Offered Rate (LIBOR) [Member] \| ShortTermDebt03242021 \| Corporate [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms	LIBOR plus 0.65
London Interbank Offered Rate (LIBOR) [Member] \| ShortTermDebt03312021.1 \| Corporate [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms	LIBOR plus 0.65
London Interbank Offered Rate (LIBOR) [Member] \| ShortTermDebt03312021.2 \| Corporate [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms	LIBOR plus 0.65
London Interbank Offered Rate (LIBOR) [Member] \| ShortTermDebt03192020 \| Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms	LIBOR plus 0.875
London Interbank Offered Rate (LIBOR) [Member] \| ShortTermDebt300 \| Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms	LIBOR plus 0.70
London Interbank Offered Rate (LIBOR) [Member] \| ShortTermDebt01252021.1 \| Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms	LIBOR plus 0.50
London Interbank Offered Rate (LIBOR) [Member] \| ShortTermDebt01252021.2 \| Commonwealth Edison Co [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms	LIBOR plus 0.75
London Interbank Offered Rate (LIBOR) [Member] \| WestMedMarch2026 \| Non-Recourse Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms	LIBOR plus 3
London Interbank Offered Rate (LIBOR) [Member] \| WestMedMarch2026 \| Exelon Generation Co L L C [Member] \| Non-Recourse Debt [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms	LIBOR plus 3

Face (par) amount of debt instrument at time of issuance.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
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+ Details

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

- Definition

Description of the interest rate as being fixed or variable, and, if variable, identification of the index or rate on which the interest rate is based and the number of points or percentage added to that index or rate to set the rate, and other pertinent information, such as frequency of rate resets.

+ References

+ Details

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

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

- Definition

Fixed interest rate related to the interest rate derivative.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeFixedInterestRate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
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+ Details

Name:	us-gaap_DerivativeNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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

- Definition

Amount of debt for which creditor does not have general recourse to the debtor but rather has recourse only to the property used for collateral in the transaction or other specific property.

+ References

No definition available.

+ Details

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

- Definition

Amount of borrowings from a bank classified as other, maturing within one year or operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-Section S99
-Paragraph 1
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+ Details

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