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Impairment of Long-lived Assets Impairment of Long-Lived Assets - Narrative (Details) - USD ($) $ in Millions | 1 Months Ended | 3 Months Ended | 9 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Mar. 31, 2016 | Jun. 30, 2018 | Jun. 30, 2017 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Sep. 30, 2017 | Dec. 31, 2018 | Sep. 30, 2018 | Dec. 31, 2017 | Sep. 30, 2015
Capital Leases Net Investment In Direct Financing Leases [Line Items] |  |  |  |  |  |  |  |  |  |  |
Tangible Asset Impairment Charges |  |  |  |  | $ 36 |  |  |  |  |  |
Property, plant and equipment, net |  |  |  |  |  |  |  | $ 76,707 |  | $ 74,202 |
Gain (Loss) on Contract Termination |  |  |  |  |  | $ 4 |  |  |  |  |
Finite-Lived Intangible Assets, Gross |  |  |  |  |  |  |  | 1,267 |  | 1,228 |
Estimated residual value of leased assets | $ 356 |  |  |  |  | 356 |  |  |  |  |
Proceeds From Lease Termination |  |  |  |  |  | $ 360 |  |  |  |  |
Wind Assets [Member] |  |  |  |  |  |  |  |  |  |  |
Capital Leases Net Investment In Direct Financing Leases [Line Items] |  |  |  |  |  |  |  |  |  |  |
Property, plant and equipment, net |  |  |  |  | 60 |  |  |  |  |  |
Property, Plant, and Equipment, Fair Value Disclosure |  |  |  |  | $ 24 |  |  |  |  |  |
Pepco Holdings LLC [Member] |  |  |  |  |  |  |  |  |  |  |
Capital Leases Net Investment In Direct Financing Leases [Line Items] |  |  |  |  |  |  |  |  |  |  |
Impairment of Long-Lived Assets to be Disposed of |  |  | $ 25 |  |  |  |  |  |  |  |
Property, plant and equipment, net |  |  |  |  |  |  |  | 13,446 |  | 12,498 |
Finite-Lived Intangible Assets, Gross |  |  |  |  |  |  |  |  |  |  | $ 25
Exelon Generation Co L L C [Member] |  |  |  |  |  |  |  |  |  |  |
Capital Leases Net Investment In Direct Financing Leases [Line Items] |  |  |  |  |  |  |  |  |  |  |
Property, plant and equipment, net |  |  |  |  |  |  |  | $ 23,981 |  | $ 24,906 |
Constellation Energy Group LLC [Member] |  |  |  |  |  |  |  |  |  |  |
Capital Leases Net Investment In Direct Financing Leases [Line Items] |  |  |  |  |  |  |  |  |  |  |
Tangible Asset Impairment Charges | $ 119 |  |  | $ 15 |  |  |  |  |  |  |
Electricity Generation Plant, Non-Nuclear [Member] |  |  |  |  |  |  |  |  |  |  |
Capital Leases Net Investment In Direct Financing Leases [Line Items] |  |  |  |  |  |  |  |  |  |  |
Impaired Assets to be Disposed of by Method Other than Sale, Carrying Value of Asset |  |  |  |  |  |  |  |  | $ 41 |  |
Impairment of Long-Lived Assets to be Disposed of |  | $ 41 | $ 460 |  |  |  | $ 460 |  |  |  |

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- Definition The estimate of the lease property's economic value at the end of the direct financing lease term excluding any amounts guaranteed by either the lessee or a third-party. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 30 -Section 50 -Paragraph 4 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=84165051&loc=d3e45377-112738 + Details
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- Definition Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275 + Details
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- Definition Gain (loss) related to the termination of a contract between the parties. The termination may be due to many causes including early termination of a lease by a lessee, a breach of contract by one party, or a failure to perform. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 + Details
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- Definition The carrying amount on the books of the entity of the impaired asset to be disposed of by a method other than sale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=84176398&loc=d3e2921-110230 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 45 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2611-110228 + Details
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- Definition The aggregate amount of write-downs for impairments recognized during the period for long-lived assets held for abandonment, exchange or sale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 45 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2611-110228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 + Details
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- Definition The cash inflow from proceeds received from lessor related to a long-term capital lease obligation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3255-108585 + Details
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- Definition Fair value portion of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19190-110258 + Details
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- Definition Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures. + 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(13)) -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 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(14)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: 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)(8)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229 + Details
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- Definition The charge against earnings resulting from the aggregate write down of tangible assets from their carrying value to their fair value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=84176398&loc=d3e2921-110230 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=64827811&loc=d3e1361-107760 + Details
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