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Derivative Financial Instruments - Narrative (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Derivative [Line Items] |  |  |  |  |
Ineffective portion recognized in income | $ 9,000 |  | $ 15,000 |  | $ 14,000
Cash collateral held | (17,000) |  |  |  |
Letters of credit held | 35,000 |  |  |  |
Derivative, Fair Value, Net | 1,000 |  | 6,000 |  |
InterestRateAndForeignExchangeContract [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative, Fair Value, Net | 3,000 |  | 5,000 |  |
Commodity Contract [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative, Fair Value, Net | 299,000 |  | 667,000 |  |
Baltimore Gas and Electric Company [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Credit exposure under off system sales | 3,000 |  |  |  |
Incremental collateral for loss of investment grade credit rating | 69,000 |  |  |  |
Exelon Generation Co L L C [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Letters of credit posted | 367,000 |  | 293,000 |  |
Cash collateral held | (47,000) |  | (35,000) |  |
Letters of credit held | 44,000 |  | 33,000 |  |
Cash collateral posted | 418,000 |  | 497,000 |  |
Incremental collateral for loss of investment grade credit rating | 2,100,000 |  | 1,800,000 |  |
Interest Rate Fair Value Hedge Asset at Fair Value | 7,000 |  |  |  |
Derivative, Collateral, Obligation to Return Cash | 2,000 |  | 4,000 |  |
Exelon Generation Co L L C [Member] | InterestRateAndForeignExchangeContract [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative, Fair Value, Net | 7,000 |  | 2,000 |  |
Exelon Generation Co L L C [Member] | InterestRateAndForeignExchangeContract [Member] | Designated as Hedging Instrument [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative, Fair Value, Net |  |  | 1,000 |  |
Exelon Generation Co L L C [Member] | Commodity Contract [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative, Fair Value, Net | $ 548,000 | [1] | $ 923,000 | [2] |
Commonwealth Edison Company [Member] | Energy Related Derivative [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Credit Derivative, Collateral Held Directly or by Third Parties | 38000000 |  |  |  |
Commonwealth Edison Company [Member] | Other Contract [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Credit Derivative, Collateral Held Directly or by Third Parties | 19000000 |  |  |  |
Commonwealth Edison Company [Member] | Renewable Energy Program [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Credit Derivative, Collateral Held Directly or by Third Parties | 31000000 |  |  |  |
Commonwealth Edison Co [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Term of contract | 20 years |  |  |  |
Incremental collateral for loss of investment grade credit rating | $ 7,000 |  |  |  |
PECO Energy Co [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Estimated Percent Of Gas Purchases Being Hedged | 20.00% |  |  |  |
Incremental collateral for loss of investment grade credit rating | $ 39,000 |  |  |  |
Delmarva Power & Light Company [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Incremental collateral for loss of investment grade credit rating | 11,000 |  |  |  |
Delmarva Power & Light Company [Member] | Energy Related Derivative [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Brokered Natural Gas Margin Revenue | $ 2,750 |  |  |  |
Minimum [Member] | Baltimore Gas and Electric Company [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Estimated Percent Of Gas Purchases Being Hedged | 10.00% |  |  |  |
Minimum [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Expected generation hedged in next twelve months | 89.00% |  |  |  |
Expected generation hedged in year two | 56.00% |  |  |  |
Expected generation hedged in year three | 32.00% |  |  |  |
Maximum [Member] | Baltimore Gas and Electric Company [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Estimated Percent Of Gas Purchases Being Hedged | 20.00% |  |  |  |
Maximum [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Expected generation hedged in next twelve months | 92.00% |  |  |  |
Expected generation hedged in year two | 59.00% |  |  |  |
Expected generation hedged in year three | 35.00% |  |  |  |
Atlantic City Electric Company [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Due From Affiliate Current Electric Utility | $ 5,000 |  |  |  |
PECO Energy Co Affiliate [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Due From Affiliate Current Electric Gas Utility | 30,000 |  |  |  |
Baltimore Gas And Electric Company Affiliate [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Due From Affiliate Current Electric Gas Utility | 24,000 |  |  |  |
Potomac Electric Power Company [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Due From Affiliate Current Electric Utility | 28,000 |  |  |  |
Delmarva Power & Light Company [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Due From Affiliate Current Electric Utility | 7,000 |  |  |  |
Commonwealth Edison Co Affiliate [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Due From Affiliate Current Electric Utility | 43,000 |  |  |  |
Derivative, Collateral, Obligation to Return Cash | $ 12,000 |  |  |  |
[1] | Current and noncurrent assets are shown net of collateral of $121 million and $51 million, respectively, and current and noncurrent liabilities are shown net of collateral of $125 million and $60 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $357 million at December 31, 2018.
[2] | Current and noncurrent assets are shown net of collateral of $169 million and $53 million, respectively, and current and noncurrent liabilities are shown net of collateral of $167 million and $77 million, respectively. The total cash collateral posted, net of cash collateral received and offset against mark-to-market assets and liabilities was $466 million at December 31, 2017.

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- Definition The expected/target percentage of future gas purchases being hedged at a gas distribution company. The percentage is calculated as the amount of hedging products divided by the planned natural gas purchases in support of projected firm sales. + References No definition available. + Details
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- Definition The percent for the expected/target percentage of future generation being hedged at an electric generation company in the next twelve months. The percentage of expected generation hedged is calculated as the amount of equivalent sales divided by the expected generation. Expected generation represents the amount of energy estimated to be generated or purchased through owned or contracted capacity. Equivalent sales represent all hedging products, which include cash-flow hedges, other derivatives and certain non-derivative contracts including sales to affiliates to serve their retail load. + References No definition available. + Details
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- Definition The percent for the expected/target percentage of future generation being hedged at an electric generation company in year three. The percentage of expected generation hedged is calculated as the amount of equivalent sales divided by the expected generation. Expected generation represents the amount of energy estimated to be generated or purchased through owned or contracted capacity. Equivalent sales represent all hedging products, which include cash-flow hedges, other derivatives and certain non-derivative contracts including sales to affiliates to serve their retail load. + References No definition available. + Details
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- Definition Incremental collateral amount required to be provided related to its financial instruments, including derivatives, non-derivatives, normal purchase normal sales contracts and applicable payables and receivables, if the credit rating is downgraded below investment grade. + References No definition available. + Details
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- Definition Revenue related to brokering natural gas. The entity realizes brokered margin as a result of buying and selling natural gas in back-to-back transactions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 24 -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62246-109447 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 23 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62136-109447 + Details
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