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Asset Retirement Obligations - Narrative (Details) - USD ($) | 3 Months Ended | 9 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Dec. 31, 2018 | Sep. 30, 2018 | Mar. 31, 2018 | Sep. 30, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Jun. 30, 2018
Asset Retirement Obligations [Line Items] |  |  |  |  |  |  |  |  |
Asset retirement obligations, noncurrent |  | $ 9,679,000,000 |  |  |  | $ 9,679,000,000 | $ 10,029,000,000 |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  | $ 20,000,000 |  | $ 2,000,000 |
Percent of additional decommissioning shortfall with recourse |  | 50.00% |  |  |  | 50.00% |  |  |
Nuclear decommissioning trust funds |  | $ 11,661,000,000 |  |  |  | $ 11,661,000,000 | 13,272,000,000 |  |
Spent Nuclear Fuel Obligation, Noncurrent |  | 1,171,000,000 |  |  |  | 1,171,000,000 | 1,147,000,000 |  |
Line of credit facility, maximum borrowing capacity | [1] | 9,704,000,000 |  |  |  | 9,704,000,000 |  |  |
Exelon Generation Co L L C [Member] |  |  |  |  |  |  |  |  |
Asset Retirement Obligations [Line Items] |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Period Increase (Decrease) |  |  |  |  | $ 180,000,000 |  |  | 34,000,000 |
Recovery Stranded Costs |  |  |  | $ 4,000,000 |  |  | 24,000,000 |  |
Asset retirement obligations, noncurrent |  | 9,450,000,000 |  |  |  | 9,450,000,000 | 9,844,000,000 |  |
Asset Retirement Obligation, Revision of Estimate |  | 203,000,000 | $ 84,000,000 |  | $ 138,000,000 | 0 |  | 0 |
Shortfall of decommissioning funds with recourse |  | 0 |  |  |  | 0 | 50,000,000 |  |
Nuclear decommissioning trust funds |  | 11,661,000,000 |  |  |  | 11,661,000,000 | 13,272,000,000 |  |
Spent Nuclear Fuel Obligation, Noncurrent |  | 1,171,000,000 |  |  |  | 1,171,000,000 | 1,147,000,000 |  |
ZionSolutions rent payable |  |  |  |  |  | 1.00 |  |  |
Line of credit facility, maximum borrowing capacity |  | $ 200,000,000 |  |  |  | $ 200,000,000 |  |  | $ 45,000,000
Annual average accretion of the ARO |  |  |  |  |  | 4.863% |  |  |
Number of years used in present value measurement |  |  |  |  |  | 30 years |  |  |
Historical five-year annual average after-tax return on NDT funds |  |  |  |  |  | 5.00% |  |  |
Exelon Generation Co L L C [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |
Asset Retirement Obligations [Line Items] |  |  |  |  |  |  |  |  |
Investment Interest Rate |  |  |  |  |  | 1000.00% |  |  |
Estimated annual after tax return on nuclear decommissioning funds |  | 5.00% |  |  |  | 5.00% |  |  |
Exelon Generation Co L L C [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |
Asset Retirement Obligations [Line Items] |  |  |  |  |  |  |  |  |
Investment Interest Rate |  |  |  |  |  | 7000.00% |  |  |
Estimated annual after tax return on nuclear decommissioning funds |  | 6.20% |  |  |  | 6.20% |  |  |
Nuclear Plant [Member] |  |  |  |  |  |  |  |  |
Asset Retirement Obligations [Line Items] |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  | $ 890,000,000 |  |  |
Nuclear Plant [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |  |  |  |  |
Asset Retirement Obligations [Line Items] |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Period Increase (Decrease) |  | $ 116,000,000 |  |  |  |  |  | $ 178,000,000 |
Asset Retirement Obligation, Revision of Estimate |  |  |  |  |  | 122,000,000 |  |  |
Decommissioning Liability, Noncurrent |  | 120,000,000 |  |  |  | 120,000,000 |  |  |
Nuclear decommissioning |  |  |  |  |  |  |  |  |
Asset Retirement Obligations [Line Items] |  |  |  |  |  |  |  |  |
Proceeds from Customers |  |  |  |  |  | 144,000,000 | 77,000,000 |  |
Nuclear decommissioning | Exelon Generation Co L L C [Member] |  |  |  |  |  |  |  |  |
Asset Retirement Obligations [Line Items] |  |  |  |  |  |  |  |  |
Asset Retirement Obligation, Period Increase (Decrease) |  |  |  |  |  | (77,000,000) | 34,000,000 |  |
Asset Retirement Obligation, Revision of Estimate |  |  | $ 772,000,000 |  |  |  | 444,000,000 |  |
Zion Station [Member] |  |  |  |  |  |  |  |  |
Asset Retirement Obligations [Line Items] |  |  |  |  |  |  |  |  |
Decommissioning Liability, Noncurrent |  | 0 |  |  |  | 0 |  |  |
Zion Station [Member] | Exelon Generation Co L L C [Member] |  |  |  |  |  |  |  |  |
Asset Retirement Obligations [Line Items] |  |  |  |  |  |  |  |  |
Decommissioning Liability, Noncurrent |  | 0 |  |  |  | 0 |  |  |
Assets, Total [Member] |  |  |  |  |  |  |  |  |
Asset Retirement Obligations [Line Items] |  |  |  |  |  |  |  |  |
Nuclear decommissioning trust funds |  | $ 12,695,000,000 |  |  |  | $ 12,695,000,000 | $ 13,349,000,000 |  |
[1] | 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.

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- Definition The interest rate for investments that have an interest rate. For fixed rate investments, this indicates the fixed interest rate. If the investment has a variable interest rate, the rate stated here may be the rate that is currently relevant. In this case the "Investment, Interest Rate is Current Rate for Variable Rate Investment Flag", "Investment, Interest Rate is Discount Rate at Purchase Flag", "Investment, Interest Rate Reflects Current Yield Flag" should be used. If one of these flags are not appropriate to explain the interest rate that is indicated, then a new flag should be added or an explanation should be included in "Investment, Additional Information". + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 12 -Sentence Column A + Details
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- Definition Amount of increase (decrease) in asset retirement obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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- Definition Amount of increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c)(4) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 35 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6392603&loc=d3e7123-110846 + Details
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- Definition Noncurrent portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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- Definition Decommission fund to pay for the costs of decontaminating and decommissioning of facilities through collection of revenues derived from utility assessments and government appropriations. Decommission fund investment for the process whereby a power station, at the end of its economic life, is taken permanently out of service and its site made available for other purposes. In the case of a nuclear station this comprises three different states of clearance. Immediately after the final closure, radioactive material such as nuclear fuel and operational waste is removed and the buildings surrounding the reactor shield are dismantled and finally the reactor itself is dismantled. + 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 210.5-02.12) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount of a decommissioning liability associated with a legal obligation that a firm incurs when it constructs or operates an asset that must eventually be withdrawn from active service. This may include operating assets such as nuclear power plants or shipping vessels. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.Y.Q2) -URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751 + Details
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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. + 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 of cash outflow from operating lease, excluding payments to bring another asset to condition and location necessary for its intended use. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918643-209977 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (g)(1) -URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918686-209980 + Details
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- Definition Revenue from billings to utility customers to recover what are also referred to as stranded assets or stranded investments. These are assets that formerly regulated utilities with monopolies on local service are allowed to recover during their transition to deregulated suppliers in competitive markets. Essentially, these investments are sunk costs, made by utilities under the old regulated system, which might not be recovered in a truly competitive marketplace. However, since they were valid investments at the time, the utilities are allowed to recover these costs from customers (for example, an investment in electrical generation assets that may not be recouped if customers are now allowed to purchase electricity from another utility). + 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 210.5-03.7) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 + Details
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- Definition Provision for the disposal costs of spent nuclear fuel from generating stations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.Y.Q2) -URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751 + Details
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