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Regulatory Matters Regulatory Matters - Estimated Commitments related to PJM Agreements (Details) - USD ($) $ in Millions | Dec. 31, 2018 | Jun. 30, 2018 | Dec. 31, 2017 | Mar. 31, 2017
--- | --- | --- | --- | ---
Other Commitments [Line Items] |  |  |  |  |
Other Receivables |  | $ 1,256 |  | $ 1,132 |
Total |  | 127 |  |  |
Accounts Payable, Current |  | 3,800 |  | 3,532 |
Regulatory Assets |  | 9,459 |  | 9,288 |
Regulatory Liabilities |  | 10,203 |  | 10,388 |
Exelon Generation Co L L C [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Other Receivables |  | 562 |  | 321 |
Accounts Payable, Current |  | 1,847 |  | 1,773 |
Commonwealth Edison Co [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Other Receivables |  | 320 |  | 266 |
Accounts Payable, Current |  | 607 |  | 568 |
Regulatory Assets |  |  |  | 1,279 |
Regulatory Liabilities |  | 6,343 |  | 6,577 |
PECO Energy Co [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Other Receivables |  | 151 |  | 105 |
Accounts Payable, Current |  | 370 |  | 370 |
Regulatory Assets |  |  |  | 410 |
Regulatory Liabilities |  | 596 |  | 690 |
Baltimore Gas and Electric Company [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Other Receivables |  | 90 |  | 94 |
Accounts Payable, Current |  | 295 |  | 265 |
Regulatory Assets |  |  |  | 571 |
Regulatory Liabilities |  | 1,269 |  | 1,163 |
Potomac Electric Power Company [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Other Receivables |  | 81 |  | 87 |
Accounts Payable, Current |  | 214 |  | 139 |
Regulatory Assets |  |  |  | 891 |
Regulatory Liabilities |  | 829 |  | 832 |
Delmarva Power & Light Company [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Other Receivables |  | 46 |  | 38 |
Accounts Payable, Current |  | 111 |  | 82 |
Regulatory Assets |  |  |  | 314 |
Regulatory Liabilities |  | 665 |  | 635 |
Atlantic City Electric Company [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Other Receivables |  | 55 |  | 56 |
Accounts Payable, Current |  | 154 |  | 118 |
Regulatory Assets |  |  |  | 430 |
Regulatory Liabilities |  | 420 |  | 422 |
Pepco Holdings LLC [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Other Receivables |  | 177 |  | 206 |
Total |  |  |  |  | $ 444
Accounts Payable, Current |  | 496 |  | 348 |
Regulatory Assets |  |  |  | 3,047 |
Regulatory Liabilities |  | 1,948 |  | $ 1,928 |
PJM Transmission Rate Design Settlement [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Other Receivables |  |  | $ 220 |  |
Accounts Payable, Current |  |  | 176 |  |
PJM Transmission Rate Design Settlement [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Other Receivables | [1] |  | 0 |  |
Accounts Payable, Current | [1] |  | 41 |  |
Accounts Receivable, Gross, Current |  | $ 16 |  |  |
PJM Transmission Rate Design Settlement [Member] | Commonwealth Edison Co [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Other Receivables |  |  | 122 |  |
Accounts Payable, Current |  |  | 0 |  |
PJM Transmission Rate Design Settlement [Member] | PECO Energy Co [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Other Receivables |  |  | 85 |  |
Accounts Payable, Current |  |  | 0 |  |
PJM Transmission Rate Design Settlement [Member] | Baltimore Gas and Electric Company [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Other Receivables |  |  | 0 |  |
Accounts Payable, Current |  |  | 51 |  |
PJM Transmission Rate Design Settlement [Member] | Potomac Electric Power Company [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Other Receivables |  |  | 0 |  |
Accounts Payable, Current |  |  | 84 |  |
PJM Transmission Rate Design Settlement [Member] | Delmarva Power & Light Company [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Other Receivables |  |  | 10 |  |
Accounts Payable, Current |  |  | 0 |  |
PJM Transmission Rate Design Settlement [Member] | Atlantic City Electric Company [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Other Receivables |  |  | 3 |  |
Accounts Payable, Current |  |  | 0 |  |
PJM Transmission Rate Design Settlement [Member] | Pepco Holdings LLC [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Other Receivables |  |  | 13 |  |
Accounts Payable, Current |  |  | 84 |  |
PJM Transmission Rate Design Settlement [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Regulatory Assets |  |  | 136 |  |
PJM Transmission Rate Design Settlement [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Regulatory Assets | [1] |  | 0 |  |
PJM Transmission Rate Design Settlement [Member] | Commonwealth Edison Co [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Regulatory Assets |  |  | 0 |  |
PJM Transmission Rate Design Settlement [Member] | PECO Energy Co [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Regulatory Assets |  |  | 0 |  |
PJM Transmission Rate Design Settlement [Member] | Baltimore Gas and Electric Company [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Regulatory Assets |  |  | 51 |  |
PJM Transmission Rate Design Settlement [Member] | Potomac Electric Power Company [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Regulatory Assets |  |  | 84 |  |
PJM Transmission Rate Design Settlement [Member] | Delmarva Power & Light Company [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Regulatory Assets |  |  | 0 |  |
PJM Transmission Rate Design Settlement [Member] | Atlantic City Electric Company [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Regulatory Assets |  |  | 1 |  |
PJM Transmission Rate Design Settlement [Member] | Pepco Holdings LLC [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Regulatory Assets |  |  | 85 |  |
PJM Transmission Rate Design Settlement [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Regulatory Liabilities |  |  | 221 |  |
PJM Transmission Rate Design Settlement [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Regulatory Liabilities | [1] |  | 0 |  |
PJM Transmission Rate Design Settlement [Member] | Commonwealth Edison Co [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Regulatory Liabilities |  |  | 122 |  |
PJM Transmission Rate Design Settlement [Member] | PECO Energy Co [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Regulatory Liabilities |  |  | 85 |  |
PJM Transmission Rate Design Settlement [Member] | Baltimore Gas and Electric Company [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Regulatory Liabilities |  |  | 0 |  |
PJM Transmission Rate Design Settlement [Member] | Potomac Electric Power Company [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Regulatory Liabilities |  |  | 0 |  |
PJM Transmission Rate Design Settlement [Member] | Delmarva Power & Light Company [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Regulatory Liabilities |  |  | 10 |  |
PJM Transmission Rate Design Settlement [Member] | Atlantic City Electric Company [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Regulatory Liabilities |  |  | 4 |  |
PJM Transmission Rate Design Settlement [Member] | Pepco Holdings LLC [Member] |  |  |  |  |
Other Commitments [Line Items] |  |  |  |  |
Regulatory Liabilities |  |  | $ 14 |  |
[1] | Does not include an offsetting receivable from New Jersey Utilities of $16 million as of December 31, 2018.

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