v3.19.1

Debt (Corporate Revolving Facility and other Letters of Credit Facilities) (Details) - USD ($) $ in Millions | 3 Months Ended |  |  |
--- | --- | --- | --- | ---
Jun. 30, 2018 | Dec. 31, 2018 | Mar. 31, 2018 | Dec. 31, 2017
Line of Credit Facility [Line Items] |  |  |  |
Letters of Credit Outstanding, Amount |  | $ 1,365 |  | $ 1,069
Amendment No. 8 [Member] | Revolving Credit Facility [Member] |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Line of Credit Facility, Increase (Decrease), Net | $ 220 |  |  |
Revolving Credit Facility [Member] |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Letters of Credit Outstanding, Amount |  | 693 |  | 629
Revolving Credit Facility [Member] | Amendment No. 6 [Member] |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Line of Credit Facility, Maximum Borrowing Capacity | $ 1,470 |  |  |
Total Letter of Credit Sublimit |  |  | $ 1,150 |
Standby Letters of Credit [Member] |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Letters of Credit Outstanding, Amount |  | 251 |  | 244
Various Project Financing Facilities [Member] |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Letters of Credit Outstanding, Amount |  | 228 |  | 196
Other Corporate Facilities [Member] |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |
Letters of Credit Outstanding, Amount |  | 193 |  | $ 0
Line of Credit Facility, Maximum Borrowing Capacity |  | $ 200 |  |

X
- Definition Total Letter of Credit Sublimit + References No definition available. + Details
Name: | cpn_TotalLetterofCreditSublimit
Namespace Prefix: | cpn_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The total amount of the contingent obligation under letters of credit outstanding as of the reporting date. + References No definition available. + Details
Name: | us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of increase (decrease) of the credit facility. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(f)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 + Details
Name: | us-gaap_LineOfCreditFacilityIncreaseDecreaseForPeriodNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- 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: | us-gaap_LineOfCreditFacilityLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- 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://fasb.org/us-gaap/role/ref/legacyRef -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
Name: | us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | us-gaap_CreditFacilityAxis=cpn_AmendmentNo.8Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_LineOfCreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_LineOfCreditFacilityAxis=cpn_AmendmentNo.6Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_CreditFacilityAxis=us-gaap_StandbyLettersOfCreditMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_CreditFacilityAxis=cpn_VariousProjectFinancingFacilitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_CreditFacilityAxis=cpn_OtherCorporateFacilitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |