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Debt (Fair Value of Debt) (Details) (USD $)
In Millions, unless otherwise specified
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Dec. 31, 2014
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Dec. 31, 2013
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| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |
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| Notes Payable, Fair Value Disclosure |
$ 2,247us-gaap_NotesPayableFairValueDisclosure |
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$ 5,317us-gaap_NotesPayableFairValueDisclosure |
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| Senior Unsecured Notes, Fair Value Disclosure |
2,832cpn_SeniorUnsecuredNotesFairValueDisclosure |
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0cpn_SeniorUnsecuredNotesFairValueDisclosure |
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| Loans Payable, Fair Value Disclosure |
2,769us-gaap_LoansPayableFairValueDisclosure |
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2,845us-gaap_LoansPayableFairValueDisclosure |
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| Notes Payable, Other Payables, Disclosure |
1,734cpn_NotesPayableOtherPayablesDisclosure |
[1] |
1,772cpn_NotesPayableOtherPayablesDisclosure |
[1] |
| Subsidiaries Term Loan |
1,540cpn_SubsidiariesTermLoan |
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1,179cpn_SubsidiariesTermLoan |
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| Debt Excluding Capital Leases |
11,122cpn_DebtExcludingCapitalLeases |
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11,113cpn_DebtExcludingCapitalLeases |
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| Reported Value Measurement [Member] |
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| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |
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| Notes Payable, Fair Value Disclosure |
2,075us-gaap_NotesPayableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember |
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4,989us-gaap_NotesPayableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember |
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| Senior Unsecured Notes, Fair Value Disclosure |
2,800cpn_SeniorUnsecuredNotesFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember |
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0cpn_SeniorUnsecuredNotesFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember |
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| Loans Payable, Fair Value Disclosure |
2,799us-gaap_LoansPayableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember |
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2,828us-gaap_LoansPayableFairValueDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember |
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| Notes Payable, Other Payables, Disclosure |
1,688cpn_NotesPayableOtherPayablesDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember |
[1] |
1,766cpn_NotesPayableOtherPayablesDisclosure
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember |
[1] |
| Subsidiaries Term Loan |
1,596cpn_SubsidiariesTermLoan
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember |
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1,191cpn_SubsidiariesTermLoan
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember |
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| Debt Excluding Capital Leases |
$ 10,958cpn_DebtExcludingCapitalLeases
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember |
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$ 10,774cpn_DebtExcludingCapitalLeases
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember |
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