XML 170 R95.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Debt and Standby Letter of Credit Facilities (Debt Outstanding) (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013 | Mar. 31, 2007 | Oct. 10, 2014
--- | --- | --- | --- | ---
Debt Instrument |  |  |  |
Debt | $ 746.6 us-gaap_LongTermDebt | $ 676.4 us-gaap_LongTermDebt |  |
SIG Senior Notes |  |  |  |
Debt Instrument |  |  |  |
Debt instrument at face value |  |  | 400.0 us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = wtm_SiriusGroupSeniorNotesMember |
Other Debt [Member] |  |  |  |
Debt Instrument |  |  |  |
Debt | 4.8 us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = wtm_OtherDebtMember | 2.1 us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = wtm_OtherDebtMember |  |
OneBeacon | 2012 OBH Senior Notes |  |  |  |
Debt Instrument |  |  |  |
Debt instrument at face value | 275.0 us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = wtm_A2012ObhSeniorNotesMember / dei_LegalEntityAxis = wtm_OnebeaconMember | 275.0 us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = wtm_A2012ObhSeniorNotesMember / dei_LegalEntityAxis = wtm_OnebeaconMember |  |
Unamortized original issue discount | (0.3)us-gaap_DebtInstrumentUnamortizedDiscount / us-gaap_DebtInstrumentAxis = wtm_A2012ObhSeniorNotesMember / dei_LegalEntityAxis = wtm_OnebeaconMember | (0.3)us-gaap_DebtInstrumentUnamortizedDiscount / us-gaap_DebtInstrumentAxis = wtm_A2012ObhSeniorNotesMember / dei_LegalEntityAxis = wtm_OnebeaconMember |  |
Debt | 274.7 us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = wtm_A2012ObhSeniorNotesMember / dei_LegalEntityAxis = wtm_OnebeaconMember | 274.7 us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = wtm_A2012ObhSeniorNotesMember / dei_LegalEntityAxis = wtm_OnebeaconMember |  |
Sirius Group | SIG Senior Notes |  |  |  |
Debt Instrument |  |  |  |
Debt instrument at face value | 400.0 us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = wtm_SiriusGroupSeniorNotesMember / dei_LegalEntityAxis = wtm_SiriusGroupMember | 400.0 us-gaap_DebtInstrumentFaceAmount / us-gaap_DebtInstrumentAxis = wtm_SiriusGroupSeniorNotesMember / dei_LegalEntityAxis = wtm_SiriusGroupMember |  |
Unamortized original issue discount | (0.3)us-gaap_DebtInstrumentUnamortizedDiscount / us-gaap_DebtInstrumentAxis = wtm_SiriusGroupSeniorNotesMember / dei_LegalEntityAxis = wtm_SiriusGroupMember | (0.4)us-gaap_DebtInstrumentUnamortizedDiscount / us-gaap_DebtInstrumentAxis = wtm_SiriusGroupSeniorNotesMember / dei_LegalEntityAxis = wtm_SiriusGroupMember |  |
Debt | 399.7 us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = wtm_SiriusGroupSeniorNotesMember / dei_LegalEntityAxis = wtm_SiriusGroupMember | 399.6 us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = wtm_SiriusGroupSeniorNotesMember / dei_LegalEntityAxis = wtm_SiriusGroupMember |  |
White Mountains | WTM Bank Facility |  |  |  |
Debt Instrument |  |  |  |
Debt | 0 us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = wtm_WtmBankFacilityMember / dei_LegalEntityAxis = wtm_WhiteMountainsMember | 0 us-gaap_LongTermDebt / us-gaap_DebtInstrumentAxis = wtm_WtmBankFacilityMember / dei_LegalEntityAxis = wtm_WhiteMountainsMember |  |
Tranzact [Member] | Tranzact Bank Facility [Member] |  |  |  |
Debt Instrument |  |  |  |
Line of Credit Facility, Fair Value of Amount Outstanding | 67.4 us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding / us-gaap_DebtInstrumentAxis = wtm_TranzactBankFacilityMember / dei_LegalEntityAxis = wtm_TranzactMember | 0 us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding / us-gaap_DebtInstrumentAxis = wtm_TranzactBankFacilityMember / dei_LegalEntityAxis = wtm_TranzactMember |  | 70.0 us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding / us-gaap_DebtInstrumentAxis = wtm_TranzactBankFacilityMember / dei_LegalEntityAxis = wtm_TranzactMember
Line of Credit Facility, Amount Outstanding | 68.7 us-gaap_LineOfCreditFacilityAmountOutstanding / us-gaap_DebtInstrumentAxis = wtm_TranzactBankFacilityMember / dei_LegalEntityAxis = wtm_TranzactMember | 0 us-gaap_LineOfCreditFacilityAmountOutstanding / us-gaap_DebtInstrumentAxis = wtm_TranzactBankFacilityMember / dei_LegalEntityAxis = wtm_TranzactMember |  |
Unamortized Debt Issuance Expense | $ (1.3)us-gaap_UnamortizedDebtIssuanceExpense / us-gaap_DebtInstrumentAxis = wtm_TranzactBankFacilityMember / dei_LegalEntityAxis = wtm_TranzactMember | $ 0 us-gaap_UnamortizedDebtIssuanceExpense / us-gaap_DebtInstrumentAxis = wtm_TranzactBankFacilityMember / dei_LegalEntityAxis = wtm_TranzactMember |  |

X
- Definition Face (par) amount of debt instrument at time of issuance. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400 + Details
Name: | us-gaap_DebtInstrumentFaceAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_DebtInstrumentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The amount of debt discount that was originally recognized at the issuance of the instrument that has yet to be amortized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 1A -URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28541-108399 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400 + Details
Name: | us-gaap_DebtInstrumentUnamortizedDiscount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount borrowed under the credit facility as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 + Details
Name: | us-gaap_LineOfCreditFacilityAmountOutstanding
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Fair value of the amount outstanding under the credit facility. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=28364263&loc=d3e13433-108611 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=28364263&loc=d3e13476-108611 + Details
Name: | us-gaap_LineOfCreditFacilityFairValueOfAmountOutstanding
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 7 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 210.5-02.22) -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 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 9 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20, 22 -Article 5 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
Name: | us-gaap_LongTermDebt
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset. + 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 210.5-02.17) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_UnamortizedDebtIssuanceExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

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

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

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

X
- Details
Name: | us-gaap_DebtInstrumentAxis=wtm_OtherDebtMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=wtm_SiriusGroupSeniorNotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |