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Debt and Credit Agreements - Summary of Short-term Borrowing Activities (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Short-term Debt [Line Items] |  |  |
Average borrowings | $ 531 | $ 823 | $ 1,125
Maximum borrowings outstanding | $ 1,237 | $ 2,147 | $ 3,076
Short-term Debt, Weighted Average Interest Rate, over Time | 2.21% | 1.32% | 0.88%
Average interest rates at year end | 2.15% | 1.24% | 1.12%
Exelon Generation Co L L C [Member] |  |  |
Short-term Debt [Line Items] |  |  |
Average borrowings | $ 37 | $ 405 | $ 536
Maximum borrowings outstanding | $ 583 | $ 1,455 | $ 1,735
Short-term Debt, Weighted Average Interest Rate, over Time | 1.96% | 1.23% | 0.94%
Average interest rates at year end | 1.96% | 1.23% | 1.14%
Commonwealth Edison Co [Member] |  |  |
Short-term Debt [Line Items] |  |  |
Average borrowings | $ 154 | $ 200 | $ 256
Maximum borrowings outstanding | $ 520 | $ 470 | $ 755
Short-term Debt, Weighted Average Interest Rate, over Time | 2.14% | 1.24% | 0.77%
Average interest rates at year end | 2.14% | 1.24% |
PECO Energy Co [Member] |  |  |
Short-term Debt [Line Items] |  |  |
Average borrowings | $ 68 | $ 2 | $ 0
Maximum borrowings outstanding | $ 350 | $ 60 | 0
Short-term Debt, Weighted Average Interest Rate, over Time | 2.24% | 1.13% |
Average interest rates at year end | 2.24% | 1.13% |
Baltimore Gas and Electric Company [Member] |  |  |
Short-term Debt [Line Items] |  |  |
Average borrowings | $ 65 | $ 54 | 143
Maximum borrowings outstanding | $ 239 | $ 165 | $ 369
Short-term Debt, Weighted Average Interest Rate, over Time | 2.18% | 1.28% | 0.77%
Average interest rates at year end | 2.18% | 1.28% | 0.95%
Pepco Holdings LLC [Member] |  |  |
Short-term Debt [Line Items] |  |  |
Short-term Bank Loans and Notes Payable | $ 500 |  |
Average borrowings |  |  | $ 153
Maximum borrowings outstanding |  |  | $ 559
Short-term Debt, Weighted Average Interest Rate, over Time |  |  | 1.03%
Potomac Electric Power Company [Member] |  |  |
Short-term Debt [Line Items] |  |  |
Average borrowings | 22 | $ 51 | $ 4
Maximum borrowings outstanding | $ 90 | $ 197 | $ 73
Short-term Debt, Weighted Average Interest Rate, over Time | 2.24% | 1.06% | 0.71%
Average interest rates at year end | 2.24% | 1.06% | 0.90%
Delmarva Power & Light Company [Member] |  |  |
Short-term Debt [Line Items] |  |  |
Average borrowings | $ 87 | $ 40 | $ 33
Maximum borrowings outstanding | $ 245 | $ 216 | $ 116
Short-term Debt, Weighted Average Interest Rate, over Time | 2.07% | 1.48% | 0.68%
Average interest rates at year end | 2.07% | 1.48% |
Atlantic City Electric Company [Member] |  |  |
Short-term Debt [Line Items] |  |  |
Short-term Bank Loans and Notes Payable | $ 125 |  |
Average borrowings | 95 | $ 30 | $ 0
Maximum borrowings outstanding | $ 210 | $ 133 | $ 5
Short-term Debt, Weighted Average Interest Rate, over Time | 2.21% | 1.43% | 0.65%
Average interest rates at year end | 2.21% | 1.43% |

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- Definition Amount of borrowings from a bank classified as other, maturing within one year or operating cycle, if longer. + References Reference 1: 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 2: 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(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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