XML 302 R184.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Commitments and Contingencies Commitments and Contingencies - Schedule of Future Rental Expense under Operating Leases (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Mar. 23, 2016 | Dec. 31, 2016 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Operating Leases Future Minimum Payments Due [Line Items] |  |  |  |  |  |
Lease and rental expense |  |  |  | $ 670 | $ 709 | $ 777
Exelon Generation Co L L C [Member] |  |  |  |  |  |
Operating Leases Future Minimum Payments Due [Line Items] |  |  |  |  |  |
Lease and rental expense | [1] |  |  | 558 | 578 | 667
Long Term Contract For Purchase Of Electric Power Capacity |  |  | $ 604 | 493 | 508 | 604
Commonwealth Edison Co [Member] |  |  |  |  |  |
Operating Leases Future Minimum Payments Due [Line Items] |  |  |  |  |  |
Lease and rental expense |  |  |  | 7 | 9 | 15
PECO Energy Co [Member] |  |  |  |  |  |
Operating Leases Future Minimum Payments Due [Line Items] |  |  |  |  |  |
Lease and rental expense |  |  |  | 10 | 9 | 7
Baltimore Gas and Electric Company [Member] |  |  |  |  |  |
Operating Leases Future Minimum Payments Due [Line Items] |  |  |  |  |  |
Lease and rental expense |  |  |  | 35 | 32 | 22
Pepco Holdings LLC [Member] | Successor [Member] |  |  |  |  |  |
Operating Leases Future Minimum Payments Due [Line Items] |  |  |  |  |  |
Lease and rental expense |  |  | $ 49 | 48 | 63 |
Pepco Holdings LLC [Member] | Predecessor [Member] |  |  |  |  |  |
Operating Leases Future Minimum Payments Due [Line Items] |  |  |  |  |  |
Lease and rental expense |  | $ 12 |  |  |  |
Potomac Electric Power Company [Member] |  |  |  |  |  |
Operating Leases Future Minimum Payments Due [Line Items] |  |  |  |  |  |
Lease and rental expense |  |  |  | 10 | 11 | 8
Delmarva Power & Light Company [Member] |  |  |  |  |  |
Operating Leases Future Minimum Payments Due [Line Items] |  |  |  |  |  |
Lease and rental expense |  |  |  | 13 | 16 | 15
Atlantic City Electric Company [Member] |  |  |  |  |  |
Operating Leases Future Minimum Payments Due [Line Items] |  |  |  |  |  |
Lease and rental expense |  |  |  | $ 8 | $ 14 | $ 13
[1] | )Includes contingent operating lease payments associated with contracted generation agreements that are not included in the minimum future operating lease payments table above. Payments made under Generation’s contracted generation lease agreements totaled $493 million, $508 million and $604 million during 2018, 2017 and 2016, respectively. Excludes contract amortization associated with purchase accounting and contract acquisition

X
- Definition Estimated cost to purchase net capacity under a long-term power purchase agreement from a production plant constructed and financed by a public utility district, cooperative or other organization. + References No definition available. + Details
Name: | exc_LongTermContractForPurchaseOfElectricPowerCapacity
Namespace Prefix: | exc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | exc_OperatingLeasesFutureMinimumPaymentsDueLineItems
Namespace Prefix: | exc_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line. + References No definition available. + Details
Name: | us-gaap_LeaseAndRentalExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=exc_ExelonGenerationCoLLCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=exc_CommonwealthEdisonCoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=exc_PecoEnergyCoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=exc_BaltimoreGasAndElectricCompanyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=exc_PepcoHoldingsLLCMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementScenarioAxis=us-gaap_SuccessorMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementScenarioAxis=us-gaap_PredecessorMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=exc_PotomacElectricPowerCompanyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=exc_DelmarvaPowerandLightCompanyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=exc_AtlanticCityElectricCompanyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |