Debt and Credit Agreements - Narrative (Details) $ in Millions	9 Months Ended
Sep. 30, 2020 USD ($)
Parent Company [Member] \| Corporate, Non-Segment [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 550
Short-term Bank Loans and Notes Payable	500
Short-term Debt [Member] \| Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Short-term Bank Loans and Notes Payable	200
DOE Project Financing, 2.82% January 5, 2037 [Member] \| Non Recourse Debt [Member]
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount	37
Long-term Line of Credit	646
Non-Recourse Debt	470
DOE Project Financing, 2.82% January 5, 2037 [Member] \| Exelon Generation Co L L C [Member] \| Non Recourse Debt [Member]
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount	37
Long-term Line of Credit	646
Non-Recourse Debt	470
ExGenRenewablesIVNov2024 [Member] \| Non Recourse Debt [Member]
Debt Instrument [Line Items]
Non-Recourse Debt	710
Long-term Debt	850
ExGenRenewablesIVNov2024 [Member] \| Exelon Generation Co L L C [Member] \| Non Recourse Debt [Member]
Debt Instrument [Line Items]
Non-Recourse Debt	710
Long-term Debt	850
ShortTermDebt300 [Member] [Member] \| Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Short-term Bank Loans and Notes Payable	300
ExGenBilat100May152020 [Member] \| Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	100
Line of Credit, Current	$ 40
London Interbank Offered Rate (LIBOR) [Member] \| Corporate, Non-Segment [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms	LIBOR plus 0.65%
Line of Credit Facility, Interest Rate Description	LIBOR plus 1.75%
London Interbank Offered Rate (LIBOR) [Member] \| Short-term Debt [Member] \| Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms	LIBOR plus 0.50%
London Interbank Offered Rate (LIBOR) [Member] \| ShortTermDebt300 [Member] [Member] \| Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate Terms	LIBOR plus 0.75%
Revolving Credit Facility [Member] \| Exelon Generation Co L L C [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 1,500
Letters of Credit Outstanding, Amount	$ 4,900

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.

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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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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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Balance Type:	credit
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- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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Balance Type:	credit
Period Type:	instant

- Definition

Fair value of the amount outstanding under the credit facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13433-108611

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- Definition

Description of the interest rate for the amounts borrowed under the credit facility, including the terms and the method for determining the interest rate (for example, fixed or variable, LIBOR plus a percentage, increasing rate, timing of interest rate resets, remarketing provisions).

+ References

+ Details

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- 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

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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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+ Details

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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

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- Definition

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

+ References

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