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Debt and Credit Agreements - Summary of Bank Commitments, Credit Facility Borrowings and Available Capacity (Details) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 30, 2018 | Jun. 30, 2018 | Dec. 31, 2017 | Mar. 31, 2016
--- | --- | --- | --- | --- | ---
Short-term Debt [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | [1] | $ 9,704 |  |  |  |
Facility draws |  | 0 |  |  |  |
Outstanding letters of credit |  | 1,696 |  |  |  |
Actual available capacity |  | 8,008 |  |  |  |
To Support Additional Commercial Paper |  | 7,687 |  |  |  |
Credit facility agreements with minority and community banks |  | 135 |  |  | $ 128 |
Revolving Credit Facility [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  |  |  |  |  | $ 500
Exelon Corporate [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Facility draws |  | 0 |  |  |  |
Outstanding letters of credit |  | 9 |  |  |  |
Actual available capacity |  | 591 |  |  |  |
Exelon Generation Co L L C [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  | 200 |  | $ 45 |  |
To Support Additional Commercial Paper |  | 4,097 |  |  |  |
Credit facility agreements with minority and community banks |  | 49 | $ 75 |  | 49 |
Exelon Generation Co L L C [Member] | Secured Debt [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Outstanding letters of credit |  | 159 |  |  | 179 |
Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Outstanding letters of credit |  | 545 |  |  | 480 |
Exelon Generation Co L L C [Member] | Letter of Credit [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Outstanding letters of credit |  | 5 |  |  |  |
Exelon Generation Co L L C [Member] | Line of Credit [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  | 150 |  |  |  |
Actual available capacity |  | 192 |  |  |  |
To Support Additional Commercial Paper |  | 0 |  |  |  |
Credit facility agreements with minority and community banks |  | 30 |  |  |  |
Commonwealth Edison Co [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Facility draws |  | 0 |  |  |  |
Outstanding letters of credit |  | 2 |  |  |  |
Actual available capacity |  | 998 |  |  |  |
To Support Additional Commercial Paper |  | 998 |  |  |  |
Credit facility agreements with minority and community banks |  | 33 |  |  | 34 |
PECO Energy Co [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Facility draws |  | 0 |  |  |  |
Outstanding letters of credit |  | 0 |  |  |  |
Actual available capacity |  | 600 |  |  |  |
To Support Additional Commercial Paper |  | 600 |  |  |  |
Credit facility agreements with minority and community banks |  | 34 |  |  | 34 |
Baltimore Gas and Electric Company [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Facility draws |  | 0 |  |  |  |
Outstanding letters of credit |  | 1 |  |  |  |
Actual available capacity |  | 599 |  |  |  |
To Support Additional Commercial Paper |  | 564 |  |  |  |
Credit facility agreements with minority and community banks |  | 5 |  |  | 5 |
Baltimore Gas and Electric Company [Member] | Letter of Credit [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Outstanding letters of credit |  | 2 |  |  |  |
Potomac Electric Power Company [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Facility draws |  | 0 |  |  |  |
Outstanding letters of credit |  | 8 |  |  |  |
Actual available capacity |  | 292 |  |  |  |
To Support Additional Commercial Paper |  | 252 |  |  |  |
Credit facility agreements with minority and community banks |  | 5 |  |  | 2 |
Pepco Holdings LLC [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  | 1,500 |  |  |  |
Delmarva Power & Light Company [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Facility draws |  | 0 |  |  |  |
Outstanding letters of credit |  | 1 |  |  |  |
Actual available capacity |  | 299 |  |  |  |
To Support Additional Commercial Paper |  | 299 |  |  |  |
Credit facility agreements with minority and community banks |  | 5 |  |  | 2 |
Atlantic City Electric Company [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Facility draws |  | 0 |  |  |  |
Outstanding letters of credit |  | 0 |  |  |  |
Actual available capacity |  | 300 |  |  |  |
To Support Additional Commercial Paper |  | 286 |  |  |  |
Credit facility agreements with minority and community banks |  | 5 |  |  | $ 2 |
Line of Credit [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | [1] | 545 |  |  |  |
Facility draws |  | 0 |  |  |  |
Outstanding letters of credit |  | 353 |  |  |  |
Line of Credit [Member] | Exelon Generation Co L L C [Member] | Secured Debt [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | [1] | 159 |  |  |  |
Facility draws |  | 0 |  |  |  |
Outstanding letters of credit |  | 119 |  |  |  |
Actual available capacity |  | 40 |  |  |  |
To Support Additional Commercial Paper |  | 0 |  |  |  |
Revolving Credit Facility [Member] | Exelon Corporate [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | [1] | 600 |  |  |  |
To Support Additional Commercial Paper |  | 591 |  |  |  |
Revolving Credit Facility [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | [1] | 5,300 |  |  |  |
Facility draws |  | 0 |  |  |  |
Outstanding letters of credit |  | 1,203 |  |  |  |
Actual available capacity |  | 4,097 |  |  |  |
Revolving Credit Facility [Member] | Commonwealth Edison Co [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | [1] | 1,000 |  |  |  |
Revolving Credit Facility [Member] | PECO Energy Co [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | [1] | 600 |  |  |  |
Revolving Credit Facility [Member] | Baltimore Gas and Electric Company [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | [1] | 600 |  |  |  |
Revolving Credit Facility [Member] | Potomac Electric Power Company [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | [1] | 300 |  |  |  |
Revolving Credit Facility [Member] | Delmarva Power & Light Company [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | [1] | 300 |  |  |  |
Revolving Credit Facility [Member] | Atlantic City Electric Company [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | [1] | 300 |  |  |  |
Maximum [Member] | Pepco Holdings LLC [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  | 900 |  |  |  |
Maximum [Member] | Delmarva Power & Light Company [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  | 0 |  |  |  |
Maximum [Member] | Atlantic City Electric Company [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |
Short-term Debt [Line Items] |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  | $ 0 |  |  |  |
[1] | Excludes $135 million of credit facility agreements arranged at minority and community banks at Generation, ComEd, PECO, BGE, Pepco, DPL and ACE with aggregate commitments of $49 million, $33 million, $34 million, $5 million, $5 million, $5 million and $5 million, respectively. These facilities expire on October 11, 2019. These facilities are solely utilized to issue letters of credit. As of December 31, 2018, letters of credit issued under these facilities totaled $5 million and $2 million for Generation and BGE, respectively.

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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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- 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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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- Definition The maximum amount of borrowing capacity under a line of credit that is available as of the balance sheet date for financing purchases of goods acquired for inventory or imminent delivery to a customer. + References No definition available. + Details
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- Definition Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + 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 Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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