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Debt and Credit Agreements - Narrative (Details) $ / shares in Units, shares in Millions | 12 Months Ended |  |  |  |  |
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Dec. 31, 2018 USD ($) MW | Dec. 31, 2017 USD ($) shares | Dec. 31, 2016 USD ($) $ / shares | Dec. 30, 2018 USD ($) | Jun. 30, 2018 USD ($) | Mar. 31, 2016 USD ($) | Oct. 23, 2015 USD ($) | Jun. 30, 2014 USD ($) $ / shares shares
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
2019 |  | $ 1,349,000,000 |  |  |  |  |  |  |  |
Long-term Debt, Current Maturities |  | 1,349,000,000 | [1] | $ 2,088,000,000 |  |  |  |  |  |
Repayments of Long-term Debt |  | 1,786,000,000 |  | 2,490,000,000 | $ 1,936,000,000 |  |  |  |  |
Line of credit facility, maximum borrowing capacity | [2] | 9,704,000,000 |  |  |  |  |  |  |  |
Outstanding letters of credit |  | 1,696,000,000 |  |  |  |  |  |  |  |
Long-term debt, gross |  | 34,911,000,000 |  | 33,657,000,000 |  |  |  |  |  |
Long-term debt |  | 35,301,000,000 |  |  |  |  |  |  |  |
Collateral amount of debt |  | 3,000,000,000 |  |  |  |  |  |  |  |
Outstanding borrowings/facility draws |  | 0 |  |  |  |  |  |  |  |
Line of Credit Facility, Current Borrowing Capacity |  | $ 135,000,000 |  | 128,000,000 |  |  |  |  |  |
Credit agreement threshold |  | 2.50 |  |  |  |  |  |  |  |
Transition Bonds [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Long-term debt, gross |  | $ 59,000,000 |  | 90,000,000 |  |  |  |  |  |
Senior Notes [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Long-term debt, gross |  | 11,285,000,000 |  | 11,285,000,000 |  |  |  |  |  |
Junior Subordinated Debt [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Long-term debt, gross |  | $ 1,150,000,000 |  | $ 1,150,000,000 |  |  |  |  |  |
Equity units issued | shares |  |  |  |  |  |  |  |  |  | 23
Conversion price | $ / shares |  |  |  |  |  |  |  |  |  | $ 50
Interest rate on long-term debt |  |  |  | 3.497% |  |  |  |  |  | 2.50%
Stock Issued During Period, Shares, Treasury Stock Reissued | shares |  |  |  | 33 |  |  |  |  |  |
Junior Subordinated Notes |  |  |  | $ 1,150,000,000 |  |  |  |  |  | $ 1,150,000,000
Loss on Reissuance, Treasury Stock |  |  |  | 1,050,000,000 |  |  |  |  |  |
Maximum [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Basis points adders for prime-based borrowings |  | 90.00% |  |  |  |  |  |  |  |
Basis points adders for LIBOR-based borrowings |  | 1.7 |  |  |  |  |  |  |  |
Maximum [Member] | Transition Bonds [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate on long-term debt |  | 5.55% |  |  |  |  |  |  |  |
Maximum [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate on long-term debt |  | 7.60% |  |  |  |  |  |  |  |
Maximum [Member] | Junior Subordinated Debt [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate on long-term debt |  | 3.50% |  |  |  |  |  |  |  |
Minimum [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate on long-term debt |  | 2.45% |  |  |  |  |  |  |  |
Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  |  |  |  |  |  |  | $ 500,000,000 |  |
Exelon Corporate [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
2019 |  | $ 0 |  |  |  |  |  |  |  |
Repayments of Long-term Debt |  | 0 |  | 569,000,000 | 46,000,000 |  |  |  |  |
Outstanding letters of credit |  | 9,000,000 |  |  |  |  |  |  |  |
Long-term debt, gross |  | 7,039,000,000 |  | 7,039,000,000 |  |  |  |  |  |
Long-term debt |  | 7,039,000,000 |  |  |  |  |  |  |  |
Outstanding borrowings/facility draws |  | 0 |  |  |  |  |  |  |  |
Exelon Corporate [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Long-term debt, gross | [3] | 5,889,000,000 |  | 5,889,000,000 |  |  |  |  |  |
Exelon Corporate [Member] | Junior Subordinated Debt [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Long-term debt, gross |  | $ 1,150,000,000 |  | 1,150,000,000 |  |  |  |  |  |
Exelon Corporate [Member] | Maximum [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate on long-term debt | [3] | 7.60% |  |  |  |  |  |  |  |
Exelon Corporate [Member] | Maximum [Member] | Junior Subordinated Debt [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate on long-term debt |  | 3.50% |  |  |  |  |  |  |  |
Exelon Corporate [Member] | Minimum [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate on long-term debt | [3] | 2.45% |  |  |  |  |  |  |  |
Exelon Corporate [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | [2] | $ 600,000,000 |  |  |  |  |  |  |  |
Exelon Generation Co L L C [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
2019 |  | 906,000,000 |  |  |  |  |  |  |  |
Long-term Debt, Current Maturities |  | 906,000,000 |  | 346,000,000 |  |  |  |  |  |
Repayments of Long-term Debt |  | 141,000,000 |  | 1,261,000,000 | 202,000,000 |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  | 200,000,000 |  |  |  |  | $ 45,000,000 |  |  |
Long-term debt, gross |  | 8,759,000,000 |  | 8,955,000,000 |  |  |  |  |  |
Long-term debt |  | 8,759,000,000 |  |  |  |  |  |  |  |
Line of Credit Facility, Current Borrowing Capacity |  | $ 49,000,000 |  | 49,000,000 |  | $ 75,000,000 |  |  |  |
Credit agreement threshold |  | 3.00 |  |  |  |  |  |  |  |
Exelon Generation Co L L C [Member] | ExGen Texas Power [Member] | Interest Rate Swap [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate on long-term debt |  | 2.34% |  |  |  |  |  |  |  |
Non-recourse debt, interest rate swap |  | $ 505,000,000 |  |  |  |  |  |  |  |
Exelon Generation Co L L C [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Long-term debt, gross |  | 6,019,000,000 |  | 6,019,000,000 |  |  |  |  |  |
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Repayments of Long-term Debt |  |  |  |  | 31,000,000 |  |  |  |  |
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | ExGen Texas Power [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Debt Instrument, Face Amount |  | 675,000,000 |  |  |  |  |  |  |  |
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | DOE Project Financing, 3.092% January 2, 2037 [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Outstanding letters of credit |  | 38,000,000 |  |  |  |  |  |  |  |
Non-recourse debt, commitment |  | $ 646,000,000 |  |  |  |  |  |  |  |
Debt, Weighted Average Interest Rate |  | 2.82% |  |  |  |  |  |  |  |
Non-recourse debt |  | $ 508,000,000 |  |  |  |  |  |  |  |
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Denver International Airport [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate on long-term debt |  | 5.50% |  |  |  |  |  |  |  |
Outstanding borrowings/facility draws |  | $ 7,000,000 |  |  |  |  |  |  |  |
Non-recourse debt |  | $ 6,000,000 |  |  |  |  |  |  |  |
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Holyoke [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate on long-term debt |  | 5.25% |  |  |  |  |  |  |  |
Outstanding borrowings/facility draws |  | $ 11,000,000 |  |  |  |  |  |  |  |
Non-recourse debt |  | 8,000,000 |  |  |  |  |  |  |  |
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Upstream Gas Property [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Repayments of Long-term Debt |  |  |  |  | 15,000,000 |  |  |  |  |
Escrow Deposit |  |  |  |  | 6,000,000 |  |  |  |  |
Gain (Loss) on Sale of Debt Investments |  |  |  |  | 37,000,000 |  |  |  |  |
Long-term debt |  | $ 15,000,000 |  | 15,000,000 |  |  |  |  |  |
Outstanding borrowings/facility draws |  |  |  |  | 22,000,000 |  |  |  |  |
Proceeds from Sales of Business, Affiliate and Productive Assets |  |  |  | 1,000,000 |  |  |  |  |  |
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | SolGen [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate on long-term debt |  | 3.93% |  |  |  |  |  |  |  |
Debt Instrument, Face Amount |  | $ 150,000,000 |  |  |  |  |  |  |  |
Non-recourse debt |  | $ 137,000,000 |  |  |  |  |  |  |  |
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Renewable Power Generation [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate on long-term debt |  | 4.11% |  |  |  |  |  |  |  |
Debt Instrument, Face Amount |  | $ 150,000,000 |  |  |  |  |  |  |  |
Non-recourse debt |  | 115,000,000 |  |  |  |  |  |  |  |
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | Continetal Wind [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  | 131,000,000 |  |  |  |  |  |  |  |
Aggregate Bank Commitments Under Unsecured Revolving Credit Facilities |  | 10,000,000 |  |  |  |  |  |  |  |
Outstanding letters of credit |  | $ 114,000,000 |  |  |  |  |  |  |  |
Interest rate on long-term debt |  | 6.00% |  |  |  |  |  |  |  |
Debt Instrument, Face Amount |  | $ 613,000,000 |  |  |  |  |  |  |  |
Generation capacity of portfolio | MW |  | 667 |  |  |  |  |  |  |  |
Non-recourse debt |  | $ 479,000,000 |  |  |  |  |  |  |  |
Exelon Generation Co L L C [Member] | Non Recourse Debt [Member] | ExGenRenewablesIVNov2024 [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate on long-term debt |  | 3.00% |  |  |  |  |  |  |  |
Long-term debt |  | $ 850,000,000 |  |  |  |  |  |  |  |
Non-recourse debt, interest rate swap |  | 636,000,000 |  |  |  |  |  |  |  |
Non-recourse debt |  | $ 834,000,000 |  |  |  |  |  |  |  |
Non-recourse debt, hedge percentage |  | 2.32% |  |  |  |  |  |  |  |
Proceeds from Issuance of Debt |  | $ 785,000,000 |  |  |  |  |  |  |  |
Proceeds from (Repayments of) Restricted Cash, Financing Activities |  | $ 50,000,000 |  |  |  |  |  |  |  |
Exelon Generation Co L L C [Member] | Maximum [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate on long-term debt |  | 7.60% |  |  |  |  |  |  |  |
Exelon Generation Co L L C [Member] | Minimum [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate on long-term debt |  | 2.95% |  |  |  |  |  |  |  |
Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | [2] | $ 5,300,000,000 |  |  |  |  |  |  |  |
Outstanding letters of credit |  | 1,203,000,000 |  |  |  |  |  |  |  |
Outstanding borrowings/facility draws |  | 0 |  |  |  |  |  |  |  |
Exelon Generation Co L L C [Member] | Line of Credit [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | [2] | 545,000,000 |  |  |  |  |  |  |  |
Outstanding letters of credit |  | 353,000,000 |  |  |  |  |  |  |  |
Outstanding borrowings/facility draws |  | 0 |  |  |  |  |  |  |  |
Exelon Generation Co L L C [Member] | Domestic Line of Credit [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  | 95,000,000 |  |  |  | $ 100,000,000 |  |  |  |
Exelon Generation Co L L C [Member] | Line of Credit [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  | 150,000,000 |  |  |  |  |  |  |  |
Line of Credit Facility, Current Borrowing Capacity |  | 30,000,000 |  |  |  |  |  |  |  |
Exelon Generation Co L L C [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Outstanding letters of credit |  | 545,000,000 |  | 480,000,000 |  |  |  |  |  |
Commonwealth Edison Co [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
2019 |  | 300,000,000 |  |  |  |  |  |  |  |
Long-term Debt, Current Maturities |  | 300,000,000 | [4] | 840,000,000 |  |  |  |  |  |
Repayments of Long-term Debt |  | 840,000,000 |  | 425,000,000 | 665,000,000 |  |  |  |  |
Outstanding letters of credit |  | 2,000,000 |  |  |  |  |  |  |  |
Long-term debt, gross |  | 8,187,000,000 |  | 7,676,000,000 |  |  |  |  |  |
Long-term debt |  | 8,393,000,000 |  |  |  |  |  |  |  |
Outstanding borrowings/facility draws |  | 0 |  |  |  |  |  |  |  |
Line of Credit Facility, Current Borrowing Capacity |  | $ 33,000,000 |  | 34,000,000 |  |  |  |  |  |
Credit agreement threshold |  | 2.00 |  |  |  |  |  |  |  |
Commonwealth Edison Co [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | [2] | $ 1,000,000,000 |  |  |  |  |  |  |  |
PECO Energy Co [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
2019 |  | 0 |  |  |  |  |  |  |  |
Repayments of Long-term Debt |  | 500,000,000 |  | 0 | 300,000,000 |  |  |  |  |
Outstanding letters of credit |  | 0 |  |  |  |  |  |  |  |
Long-term debt, gross |  | 3,125,000,000 |  | 2,925,000,000 |  |  |  |  |  |
Long-term debt |  | 3,309,000,000 |  |  |  |  |  |  |  |
Outstanding borrowings/facility draws |  | 0 |  |  |  |  |  |  |  |
Line of Credit Facility, Current Borrowing Capacity |  | $ 34,000,000 |  | 34,000,000 |  |  |  |  |  |
Credit agreement threshold |  | 2.00 |  |  |  |  |  |  |  |
PECO Energy Co [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | [2] | $ 600,000,000 |  |  |  |  |  |  |  |
Baltimore Gas and Electric Company [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
2019 |  | 0 |  |  |  |  |  |  |  |
Repayments of Long-term Debt |  | 0 |  | 41,000,000 | $ 379,000,000 |  |  |  |  |
Outstanding letters of credit |  | 1,000,000 |  |  |  |  |  |  |  |
Long-term debt, gross |  | 2,900,000,000 |  | 2,600,000,000 |  |  |  |  |  |
Long-term debt |  | 2,900,000,000 |  |  |  |  |  |  |  |
Outstanding borrowings/facility draws |  | 0 |  |  |  |  |  |  |  |
Line of Credit Facility, Current Borrowing Capacity |  | $ 5,000,000 |  | 5,000,000 |  |  |  |  |  |
Preferred Stock, Redemption Price Per Share | $ / shares |  |  |  |  | $ 100 |  |  |  |  |
Credit agreement threshold |  | 2.00 |  |  |  |  |  |  |  |
Baltimore Gas and Electric Company [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Long-term debt, gross |  | $ 2,900,000,000 |  | 2,600,000,000 |  |  |  |  |  |
Baltimore Gas and Electric Company [Member] | Maximum [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate on long-term debt |  | 6.35% |  |  |  |  |  |  |  |
Baltimore Gas and Electric Company [Member] | Minimum [Member] | Senior Notes [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate on long-term debt |  | 2.40% |  |  |  |  |  |  |  |
Baltimore Gas and Electric Company [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | [2] | $ 600,000,000 |  |  |  |  |  |  |  |
Pepco Holdings LLC [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
2019 |  | 125,000,000 |  |  |  |  |  |  |  |
Repayments of Long-term Debt |  | 299,000,000 |  | 169,000,000 |  |  |  |  |  |
Long-term debt, gross |  | 5,636,000,000 |  | 5,189,000,000 |  |  |  |  |  |
Long-term debt |  | 5,636,000,000 |  |  |  |  |  |  |  |
Short-term Bank Loans and Notes Payable |  | $ 500,000,000 |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate Terms |  | LIBOR plus 1% |  |  |  |  |  |  |  |
Pepco Holdings LLC [Member] | Transition Bonds [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Long-term debt, gross | [5] | $ 59,000,000 |  | 90,000,000 |  |  |  |  |  |
Pepco Holdings LLC [Member] | Maximum [Member] | Transition Bonds [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate on long-term debt | [5] | 5.55% |  |  |  |  |  |  |  |
Pepco Holdings LLC [Member] | Minimum [Member] | Transition Bonds [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate on long-term debt | [5] |  |  |  |  |  |  |  |  |
Pepco Holdings LLC [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  | $ 1,500,000,000 |  |  |  |  |  |  |  |
Pepco Holdings LLC [Member] | Revolving Credit Facility [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  | 900,000,000 |  |  |  |  |  |  |  |
Potomac Electric Power Company [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
2019 |  | 15,000,000 |  |  |  |  |  |  |  |
Repayments of Long-term Debt |  | 14,000,000 |  | 13,000,000 | $ 11,000,000 |  |  |  |  |
Outstanding letters of credit |  | 8,000,000 |  |  |  |  |  |  |  |
Long-term debt, gross |  | 2,751,000,000 |  | 2,570,000,000 |  |  |  |  |  |
Long-term debt |  | 2,751,000,000 |  |  |  |  |  |  |  |
Outstanding borrowings/facility draws |  | 0 |  |  |  |  |  |  |  |
Line of Credit Facility, Current Borrowing Capacity |  | $ 5,000,000 |  | 2,000,000 |  |  |  |  |  |
Credit agreement threshold |  | 2.00 |  |  |  |  |  |  |  |
Potomac Electric Power Company [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | [2] | $ 300,000,000 |  |  |  |  |  |  |  |
Delmarva Power & Light Company [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
2019 |  | 91,000,000 |  |  |  |  |  |  |  |
Long-term Debt, Current Maturities |  | 79,000,000 |  | 79,000,000 |  |  |  |  |  |
Repayments of Long-term Debt |  | 4,000,000 |  | 40,000,000 | 100,000,000 |  |  |  |  |
Outstanding letters of credit |  | 1,000,000 |  |  |  |  |  |  |  |
Long-term debt, gross |  | 1,504,000,000 |  | 1,309,000,000 |  |  |  |  |  |
Long-term debt |  | 1,504,000,000 |  |  |  |  |  |  |  |
Outstanding borrowings/facility draws |  | 0 |  |  |  |  |  |  |  |
Line of Credit Facility, Current Borrowing Capacity |  | $ 5,000,000 |  | 2,000,000 |  |  |  |  |  |
Credit agreement threshold |  | 2.00 |  |  |  |  |  |  |  |
Delmarva Power & Light Company [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | [2] | $ 300,000,000 |  |  |  |  |  |  |  |
Delmarva Power & Light Company [Member] | Revolving Credit Facility [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  | 0 |  |  |  |  |  |  |  |
Atlantic City Electric Company [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
2019 |  | 18,000,000 |  |  |  |  |  |  |  |
Repayments of Long-term Debt |  | 281,000,000 |  | 35,000,000 | $ 48,000,000 |  |  |  |  |
Outstanding letters of credit |  | 0 |  |  |  |  |  |  |  |
Long-term debt, gross |  | 1,196,000,000 |  | 1,127,000,000 |  |  |  |  |  |
Long-term debt |  | 1,196,000,000 |  |  |  |  |  |  |  |
Outstanding borrowings/facility draws |  | 0 |  |  |  |  |  |  |  |
Short-term Bank Loans and Notes Payable |  | $ 125,000,000 |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate Terms |  | LIBOR plus 0.55% |  |  |  |  |  |  |  |
Line of Credit Facility, Current Borrowing Capacity |  | $ 5,000,000 |  | 2,000,000 |  |  |  |  |  |
Credit agreement threshold |  | 2.00 |  |  |  |  |  |  |  |
Atlantic City Electric Company [Member] | Transition Bonds [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
2019 |  | $ 18,000,000 |  |  |  |  |  |  |  |
Long-term debt, gross | [6] | $ 59,000,000 |  | $ 90,000,000 |  |  |  |  |  |
Atlantic City Electric Company [Member] | Maximum [Member] | Transition Bonds [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate on long-term debt | [6] | 5.55% |  |  |  |  |  |  |  |
Atlantic City Electric Company [Member] | Revolving Credit Facility [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity | [2] | $ 300,000,000 |  |  |  |  |  |  |  |
Atlantic City Electric Company [Member] | Revolving Credit Facility [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  | 0 |  |  |  |  |  |  |  |
Corporate, Non-Segment [Member] | Exelon Corporate [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Short-term Bank Loans and Notes Payable |  | $ 500,000,000 |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate Terms |  | LIBOR plus 1% |  |  |  |  |  |  |  |
CENG [Member] | Exelon Generation Co L L C [Member] | Domestic Line of Credit [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  | $ 200,000,000 |  |  |  |  |  |  |  |
CENG [Member] | Exelon Generation Co L L C [Member] | Line of Credit [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  |  |  |  |  |  |  |  | $ 100,000,000 |
[1] | In January 2019, $300 million of ComEd long-term debt due within one year was paid in full.
[2] | 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.
[3] | Senior unsecured notes include mirror debt that is held on both Generation and Exelon Corporation's balance sheets.
[4] | In January 2019, the $300 million balance was paid in full.
[5] | Transition bonds are recorded as part of Long-term debt within ACE's Consolidated Balance Sheets.
[6] | Maturities of ACE's Transition Bonds outstanding at December 31, 2018 are $18 million in 2019, $20 million in 2020 and $21 million in 2021.

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- Definition Aggregate bank commitments as of the balance sheet date under a credit facility agreement in which loan proceeds can continuously be obtained following repayments, but the total amount borrowed cannot exceed a specified maximum amount. Terms typically include interest rate, collateral required, guarantees required, repayment requirements, and restrictions on use of assets and activities of the entity. + References No definition available. + Details
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- Definition Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt. + 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 Amount of assets pledged to secure a debt instrument. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 50 -Paragraph 3 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823 + Details
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- Definition Contractual interest rate for funds borrowed, under the debt 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(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition The designation of funds furnished by a borrower to a lender to assure future payments of the borrower's real estate taxes and insurance obligations with respect to a mortgaged property. Escrow deposits may be made for a variety of other purposes such as earnest money and contingent payments. This element excludes replacement reserves which are an escrow separately provided for within the US GAAP taxonomy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.10) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + 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 Description of the conditions for borrowing under the credit facility including the nature of any restrictions. + 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 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/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(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 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: 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 + Details
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