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Investment Securities (Mortgage-backed Asset Securities Table) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 5,957.2us-gaap_InvestmentsFairValueDisclosure	$ 5,991.4us-gaap_InvestmentsFairValueDisclosure	$ 6,736.7us-gaap_InvestmentsFairValueDisclosure	$ 6,766.5us-gaap_InvestmentsFairValueDisclosure
Commercial Mortgage Backed Securities Fixed Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	165.6us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = wtm_CommercialMortgageBackedSecuritiesFixedRateMember
Government National Mortgage Association Certificates and Obligations (GNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	373.0us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember	411.2us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
Federal National Mortgage Association Certificates and Obligations (FNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	35.2us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember	36.6us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	38.9us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember	49.6us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	447.1us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember	497.4us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	194.3us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember	131.2us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember
Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	292.2us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialMortgageBackedSecuritiesMember	236.9us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialMortgageBackedSecuritiesMember
Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	486.5us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember	368.1us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
Collateralized Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	933.6us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember	865.5us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember
Collateralized Credit Card Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	472.9us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CollateralizedCreditCardSecuritiesMember	522.2us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CollateralizedCreditCardSecuritiesMember
Collateralized Auto Loans
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	537.2us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CollateralizedAutoLoansMember	289.4us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CollateralizedAutoLoansMember
Collateralized Securities, Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	154.4us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CollateralizedSecuritiesOtherMember	163.8us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CollateralizedSecuritiesOtherMember
Asset-backed Securities, Securitized Loans and Receivables
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,164.5us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember	975.4us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember
Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	2,098.1us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember	1,840.9us-gaap_InvestmentsFairValueDisclosure / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember
Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	4,594.0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member	4,638.0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member	4,727.5us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member	4,982.2us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Level 2 Inputs | Government National Mortgage Association Certificates and Obligations (GNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	373.0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember	411.2us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
Level 2 Inputs | Federal National Mortgage Association Certificates and Obligations (FNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	35.2us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember	36.6us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember
Level 2 Inputs | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	38.9us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember	49.6us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember
Level 2 Inputs | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	447.1us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember	497.4us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Level 2 Inputs | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	147.2us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember	131.2us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember
Level 2 Inputs | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	271.6us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialMortgageBackedSecuritiesMember	236.9us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialMortgageBackedSecuritiesMember
Level 2 Inputs | Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	418.8us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember	368.1us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
Level 2 Inputs | Collateralized Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	865.9us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember	865.5us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember
Level 2 Inputs | Collateralized Credit Card Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	472.9us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CollateralizedCreditCardSecuritiesMember	522.2us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CollateralizedCreditCardSecuritiesMember
Level 2 Inputs | Collateralized Auto Loans
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	537.2us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CollateralizedAutoLoansMember	289.4us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CollateralizedAutoLoansMember
Level 2 Inputs | Collateralized Securities, Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	154.4us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CollateralizedSecuritiesOtherMember	163.8us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CollateralizedSecuritiesOtherMember
Level 2 Inputs | Asset-backed Securities, Securitized Loans and Receivables
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,164.5us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember	975.4us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember
Level 2 Inputs | Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	2,030.4us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember	1,840.9us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember
Level 3 Inputs | Government National Mortgage Association Certificates and Obligations (GNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember	0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_GovernmentNationalMortgageAssociationCertificatesAndObligationsGNMAMember
Level 3 Inputs | Federal National Mortgage Association Certificates and Obligations (FNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember	0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_FederalNationalMortgageAssociationCertificatesAndObligationsFNMAMember
Level 3 Inputs | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember	0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_FederalHomeLoanMortgageCorporationCertificatesAndObligationsFHLMCMember
Level 3 Inputs | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember	0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Level 3 Inputs | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	47.1us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember	0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember
Level 3 Inputs | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	20.6us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialMortgageBackedSecuritiesMember	0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialMortgageBackedSecuritiesMember
Level 3 Inputs | Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	67.7us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember	0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
Level 3 Inputs | Collateralized Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	67.7us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember	0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesMember
Level 3 Inputs | Collateralized Credit Card Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CollateralizedCreditCardSecuritiesMember	0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CollateralizedCreditCardSecuritiesMember
Level 3 Inputs | Collateralized Auto Loans
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CollateralizedAutoLoansMember	0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CollateralizedAutoLoansMember
Level 3 Inputs | Collateralized Securities, Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CollateralizedSecuritiesOtherMember	0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CollateralizedSecuritiesOtherMember
Level 3 Inputs | Asset-backed Securities, Securitized Loans and Receivables
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember	0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember
Level 3 Inputs | Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 67.7us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember	$ 0us-gaap_InvestmentsFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember
Maximum | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Loans and Leases Receivable, Ratio of Nonperforming Loans to All Loans	1.00%us-gaap_LoansAndLeasesReceivableRatioOfNonperformingLoansToAllLoans / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialMortgageBackedSecuritiesMember / us-gaap_RangeAxis = us-gaap_MaximumMember

X

- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Available-for-Sale Securities

-URI http://asc.fasb.org/extlink&oid=6505594



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Trading Securities

-URI http://asc.fasb.org/extlink&oid=6526789



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Subparagraph a, f, g

-Article 7



Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 35

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e24584-111560

+ Details

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X

- Definition

Reflects the percentage derived from dividing impaired loans on which interest has ceased to be accrued by total loans.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Details

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- Details

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- Details

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