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Commitments and Contingencies Commitments and Contingencies - Narrative (Details) |  |  |  | 3 Months Ended | 12 Months Ended |
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Nov. 04, 2016 | Nov. 01, 2015 USD ($) | Sep. 23, 2015 USD ($) | Dec. 31, 2018 USD ($) employee Open_claim MGPSite | Sep. 30, 2018 USD ($) | Dec. 31, 2017 USD ($) MW | Dec. 31, 2018 USD ($) employee Open_claim MGPSite MW | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Feb. 17, 2012 USD ($)
Commitments and Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Leases, Future Minimum Payments Due | [1],[2] |  |  |  | $ 1,378,000,000 |  |  | $ 1,378,000,000 |  |  |
Direct Investment Commitment |  |  |  |  |  |  |  |  |  |  | $ 1,000,000,000
Power Volume | MW |  |  |  |  |  |  | 10 | 220 |  |  |
Business Acquisition Residual Commitment | MW |  |  |  |  |  |  | 55 |  |  |  |
Loss Contingency, Loss in Period |  |  |  |  |  |  |  |  |  | $ 50,000,000 |
Nontrade Receivables, Current | [3] |  |  |  | 124,000,000 |  | $ 94,000,000 | $ 124,000,000 | 94,000,000 |  |
Nontrade Receivables, Noncurrent | [4] |  |  |  | 15,000,000 |  | 15,000,000 | 15,000,000 | 15,000,000 |  |
Accounts Payable, Other, Current | [3],[5] |  |  |  | (17,000,000) |  | (11,000,000) | (17,000,000) | (11,000,000) |  |
DOE Spent Nuclear Fuel One Time Fee |  |  |  |  | 34,000,000 |  |  | 34,000,000 |  |  |
Operating Expenses | [6] |  |  |  |  |  |  | 32,143,000,000 | 29,619,000,000 | 28,106,000,000 |
Exelon Generation Co L L C [Member] |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Leases, Future Minimum Payments Due | [1],[2] |  |  |  | 763,000,000 |  |  | 763,000,000 |  |  |
Direct Investment Commitment |  |  |  |  |  |  |  |  |  |  |
Entity Number of Employees | employee |  |  |  |  | 1,500 |  |  | 1,500 |  |  |
Leasehold Improvements, Gross |  |  |  |  | $ 90,000,000 |  |  | $ 90,000,000 |  |  |
Lessee, Operating Lease, Term of Contract |  | 20 years |  |  |  |  |  |  |  |  |
Costs Incurred, Development Costs |  |  |  |  |  |  |  | 458,000,000 |  |  |
Nuclear financial protection pool value |  |  |  |  | 450,000,000 |  |  | 450,000,000 |  |  |
Maximum recovery limit from a nuclear industry mutual insurance company in the event of multiple losses |  |  |  |  | 13,600,000,000 |  |  | 13,600,000,000 |  |  |
Maximum annual assessment payment mandated by Price-Anderson Act for a nuclear incident |  |  |  |  | 3,100,000,000 |  |  | 3,100,000,000 |  |  |
Mutual Insurance Total Retrospective Premium Obligation |  |  |  |  | 345,000,000 |  |  | 345,000,000 |  |  |
Mutual Replacement Power Cost Insurance Maximum Retrospective Premium Obligation |  |  |  |  | 3,200,000,000 |  |  | 3,200,000,000 |  |  |
Cost of spent nuclear fuel disposal per kWh of net nuclear generation |  |  |  |  | 0.001 |  |  | 0.001 |  |  |
Spent Nuclear Fuel Storage Reimbursement | [7] |  |  |  |  |  |  | 1,274,000,000 |  |  |
Spent Nuclear Fuel Storage Reimbursement Net Co Owners | [7],[8] |  |  |  |  |  |  | 1,100,000,000 |  |  |
DOE Spent Nuclear Fuel One Time Fee |  |  |  |  | 277,000,000 |  |  | 277,000,000 |  |  |
DOE Spent Nuclear Fuel One Time Fee With Interest |  |  |  |  | 1,171,000,000 |  | 1,147,000,000 | $ 1,171,000,000 | 1,147,000,000 |  |
Spent Nuclear Fuel Treasury Interest Rate |  |  |  |  |  |  |  | 2.351% |  |  |
Loss Contingency Accrual, Provision |  |  |  |  | 20,000,000 |  |  |  |  |  |
Environmental loss contingencies |  |  |  |  |  |  | 90,000,000 |  | 90,000,000 |  |
Asbestos Liability Reserve |  |  |  |  | $ 79,000,000 |  | 78,000,000 | $ 79,000,000 | 78,000,000 |  |
Open Asbestos Liability Claims | Open_claim |  |  |  |  | 238 |  |  | 238 |  |  |
Exelon Generation Co L L C [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Direct Investment Commitment |  |  |  |  | $ 450,000,000 |  |  | $ 450,000,000 |  |  |
Business Acquisition, Expected New Generation Mwh | MW |  |  |  |  |  |  |  | 285 |  |  |
Exelon Generation Co L L C [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Direct Investment Commitment |  |  |  |  | 500,000,000 |  |  | $ 500,000,000 |  |  |
Business Acquisition, Expected New Generation Mwh | MW |  |  |  |  |  |  |  | 300 |  |  |
Exelon Generation Co L L C [Member] | West Lake [Member] |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Loss Contingency Accrual, Provision |  |  |  |  | 280,000,000 |  |  |  |  |  |
Exelon Generation Co L L C [Member] | Nuclear Insurance Premiums [Member] |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Nuclear insurance liability limit per incident |  |  |  |  | 14,100,000,000 |  |  | $ 14,100,000,000 |  |  |
Exelon Generation Co L L C [Member] | Nuclear Insurance Premiums [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Nuclear financial protection pool value |  |  |  |  |  | $ 454,000,000 |  |  |  |  |
Exelon Generation Co L L C [Member] | Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member] |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Mutual Property Insurance Distribution To Members |  |  |  |  | 58,000,000 |  | 60,000,000 | 58,000,000 | 60,000,000 | $ 21,000,000 |
Commonwealth Edison Co [Member] |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Leases, Future Minimum Payments Due | [2],[9] |  |  |  | 23,000,000 |  |  | 23,000,000 |  |  |
Direct Investment Commitment |  |  |  |  |  |  |  |  |  |  |
Total number of MGP sites | MGPSite |  |  |  |  | 42 |  |  | 42 |  |  |
Sites approved for clean-up | MGPSite |  |  |  |  | 21 |  |  | 21 |  |  |
Sites under study/remediation | MGPSite |  |  |  |  | 21 |  |  | 21 |  |  |
Other Increase (Decrease) in Environmental Liabilities |  |  |  |  |  | $ 48,000,000 |  |  |  |  |
PECO Energy Co [Member] |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Leases, Future Minimum Payments Due | [2],[9] |  |  |  | $ 25,000,000 |  |  | $ 25,000,000 |  |  |
Direct Investment Commitment |  |  |  |  |  |  |  |  |  |  |
Total number of MGP sites | MGPSite |  |  |  |  | 26 |  |  | 26 |  |  |
Sites approved for clean-up | MGPSite |  |  |  |  | 17 |  |  | 17 |  |  |
Sites under study/remediation | MGPSite |  |  |  |  | 9 |  |  | 9 |  |  |
Baltimore Gas and Electric Company [Member] |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Leases, Future Minimum Payments Due | [2],[9],[10],[11] |  |  |  | $ 143,000,000 |  |  | $ 143,000,000 |  |  |
Direct Investment Commitment |  |  |  |  |  |  |  |  |  |  |
Total number of MGP sites | MGPSite |  |  |  |  | 13 |  |  | 13 |  |  |
Sites approved for clean-up | MGPSite |  |  |  |  | 9 |  |  | 9 |  |  |
Sites under study/remediation | MGPSite |  |  |  |  | 4 |  |  | 4 |  |  |
Common Equity Tier One Capital Ratio |  |  |  |  | 48.00% |  |  | 48.00% |  |  |
Occupancy, Net |  |  | $ 42,000,000 | $ 12,000,000 |  |  |  |  |  |  |
Operating Leases, Income Statement, Initial Direct Costs |  |  |  |  |  |  | 25,000,000 |  |  |  |
Oil and Gas Property, Lease Operating Expense |  |  |  |  |  |  | 29,000,000 |  |  |  |
Operating Expenses |  |  |  |  |  |  | 28,000,000 |  |  |  |
Pepco Holdings LLC [Member] |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Leases, Future Minimum Payments Due | [2] |  |  |  | $ 377,000,000 |  |  | $ 377,000,000 |  |  |
Direct Investment Commitment |  |  |  |  |  |  |  |  |  |  |
Potomac Electric Power Company [Member] |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Leases, Future Minimum Payments Due | [2] |  |  |  | 86,000,000 |  |  | 86,000,000 |  |  |
Direct Investment Commitment |  |  |  |  |  |  |  |  |  |  |
Accrued Liabilities and Other Liabilities |  |  |  |  | 30,000,000 |  | 28,000,000 | 30,000,000 | 28,000,000 |  |
Delmarva Power & Light Company [Member] |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Leases, Future Minimum Payments Due | [2],[9] |  |  |  | 96,000,000 |  |  | 96,000,000 |  |  |
Direct Investment Commitment |  |  |  |  |  |  |  |  |  |  |
Total number of MGP sites | MGPSite |  |  |  |  | 3 |  |  | 3 |  |  |
Sites approved for clean-up | MGPSite |  |  |  |  | 2 |  |  | 2 |  |  |
Common Equity Tier One Capital Ratio |  |  |  |  | 48.00% |  |  | 48.00% |  |  |
Atlantic City Electric Company [Member] |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating Leases, Future Minimum Payments Due | [2] |  |  |  | $ 32,000,000 |  |  | $ 32,000,000 |  |  |
Direct Investment Commitment |  |  |  |  |  |  |  |  |  |  |
Common Equity Tier One Capital Ratio |  |  |  |  | 30.00% |  |  | 30.00% |  |  |
Open Claims [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Asbestos Liability Reserve |  |  |  |  | $ 24,000,000 |  |  | $ 24,000,000 |  |  |
Estimated Future Claims [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |  |  |  |  |  |  |
Commitments and Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |
Asbestos Liability Reserve |  |  |  |  | $ 55,000,000 |  |  | $ 55,000,000 |  |  |
[1] | )Excludes Generation’s contingent operating lease payments associated with contracted generation agreement
[2] | )Includes amounts related to shared use land arrangement
[3] | )Recorded in Accounts receivable, other.
[4] | )Recorded in Deferred debits and other assets, oth
[5] | )Non-CENG amounts owed to co-owners are recorded in Accounts receivable, other. CENG amounts owed to co-owners are recorded in Accounts payable. Represents amounts owed to the co-owners of Peach Bottom, Quad Cities, and Nine Mile Point Unit 2 generating facilities
[6] | Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses in the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 23 — Supplemental Financial Information for additional information on total utility taxes.
[7] | )Includes $53 and $49, respectively, for amounts received since April 1, 2014, for costs incurred under the CENG DOE Settlement Agreements prior to the consolidation of CEN
[8] | )Total after considering amounts due to co-owners of certain nuclear stations and to the former owner of Oyster Cree
[9] | )Amounts related to certain real estate leases and railroad licenses effectively have indefinite payment periods. As a result, ComEd, PECO, BGE and DPL have excluded these payments from the remaining years as such amounts would not be meaningful. ComEd's, PECO’s, BGE’s and DPL's average annual obligation for these arrangements, included in each of the years 2019 - 2023, was $3 million, $5 million, $1 million and $1 million respectivel
[10] | )The BGE column above includes minimum future lease payments associated with a 6-year lease for the Baltimore City conduit system that became effective during the fourth quarter of 2016. BGE's total commitments under the lease agreement are $26 million, $28 million, $28 million and $14 million related to years 2019 - 2022 , respectivel
[11] | )The BGE column above includes minimum future lease payments associated with a 6-year lease for the Baltimore City conduit system that became effective during the fourth quarter of 2016. BGE's total commitments under the lease agreement are $26 million, $28 million, $28 million and $14 million related to years 2019 - 2022 , respectivel

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