XML 137 R80.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Investment Securities (Cost and Amortized Cost Maturity Schedule) (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014
--- | ---
Trading Securities by Maturity Cost or Amortized Cost |
Cost or amortized cost | $ 4,664.8 wtm_TradingSecuritiesAmortizedCost
Trading Securities by Maturity, Fair Value |
Trading Securities | 4,796.5 us-gaap_TradingSecurities
Fixed Maturities and Convertible Fixed Maturities Excluding A B S M B S and Preferred Stock |
Trading Securities by Maturity Cost or Amortized Cost |
Due in one year or less | 331.2 wtm_TradingSecuritiesMaturitiesWithinOneYearCostOrAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = wtm_FixedMaturitiesAndConvertibleFixedMaturitiesExcludingMortgageBackedSecuritesAssetBackedSecuritiesAndPreferredStockMember
Due after one year through five years | 1,968.3 wtm_TradingSecuritiesMaturitiesAfterOneThroughFiveYearsCostOrAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = wtm_FixedMaturitiesAndConvertibleFixedMaturitiesExcludingMortgageBackedSecuritesAssetBackedSecuritiesAndPreferredStockMember
Due after five years through ten years | 434.4 wtm_TradingSecuritiesMaturitiesAfterFiveThroughTenYearsCostOrAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = wtm_FixedMaturitiesAndConvertibleFixedMaturitiesExcludingMortgageBackedSecuritesAssetBackedSecuritiesAndPreferredStockMember
Due after ten years | 40.2 wtm_TradingSecuritiesMaturitiesAfterTenYearsCostOrAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = wtm_FixedMaturitiesAndConvertibleFixedMaturitiesExcludingMortgageBackedSecuritesAssetBackedSecuritiesAndPreferredStockMember
Trading Securities by Maturity, Fair Value |
Due in one year or less | 337.5 wtm_TradingSecuritiesMaturitiesWithinOneYearNetCarryingAmount / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = wtm_FixedMaturitiesAndConvertibleFixedMaturitiesExcludingMortgageBackedSecuritesAssetBackedSecuritiesAndPreferredStockMember
Due after one year through five years | 2,032.3 wtm_TradingSecuritiesMaturitiesAfterOneThroughFiveYearsNetCarryingAmount / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = wtm_FixedMaturitiesAndConvertibleFixedMaturitiesExcludingMortgageBackedSecuritesAssetBackedSecuritiesAndPreferredStockMember
Due after five years through ten years | 453.9 wtm_TradingSecuritiesMaturitiesAfterFiveThroughTenYearsNetCarryingAmount / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = wtm_FixedMaturitiesAndConvertibleFixedMaturitiesExcludingMortgageBackedSecuritesAssetBackedSecuritiesAndPreferredStockMember
Due after ten years | 46.1 wtm_TradingSecuritiesMaturitiesAfterTenYearsNetCarryingAmount / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = wtm_FixedMaturitiesAndConvertibleFixedMaturitiesExcludingMortgageBackedSecuritesAssetBackedSecuritiesAndPreferredStockMember
Mortgage-backed and asset-backed securities |
Trading Securities by Maturity Cost or Amortized Cost |
Trading Securities, Maturities without Single Maturity Date, Amortized Cost | 1,811.1 wtm_TradingSecuritiesMaturitiesWithoutSingleMaturityDateAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember
Trading Securities by Maturity, Fair Value |
Trading Securities, Maturities without Single Maturity Date, Carrying Value | 1,840.9 wtm_TradingSecuritiesMaturitiesWithoutSingleMaturityDateCarryingValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember
Preferred stocks |
Trading Securities by Maturity Cost or Amortized Cost |
Trading Securities, Maturities without Single Maturity Date, Amortized Cost | 79.6 wtm_TradingSecuritiesMaturitiesWithoutSingleMaturityDateAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_PreferredStockMember
Trading Securities by Maturity, Fair Value |
Trading Securities, Maturities without Single Maturity Date, Carrying Value | $ 85.8 wtm_TradingSecuritiesMaturitiesWithoutSingleMaturityDateCarryingValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_PreferredStockMember

X
- Definition Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26626-111562 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 210.9-03.4) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789 + Details
Name: | us-gaap_TradingSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the cost of trading securities, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References No definition available. + Details
Name: | wtm_TradingSecuritiesAmortizedCost
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | wtm_TradingSecuritiesByMaturityCostOrAmortizedCostAbstract
Namespace Prefix: | wtm_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | wtm_TradingSecuritiesByMaturityFairValueAbstract
Namespace Prefix: | wtm_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition This item represents securities, at cost, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments, as defined), and fair value hedge accounting adjustments, if any, which are expected to mature after five years and through ten years from the balance sheet date classified as trading. + References No definition available. + Details
Name: | wtm_TradingSecuritiesMaturitiesAfterFiveThroughTenYearsCostOrAmortizedCost
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the carrying value of debt securities which are expected to mature after five years and through ten years from the balance sheet date classified as trading. + References No definition available. + Details
Name: | wtm_TradingSecuritiesMaturitiesAfterFiveThroughTenYearsNetCarryingAmount
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents securities, at cost, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments, as defined), and fair value hedge accounting adjustments, if any, which are expected to mature after one year and through five years from the balance sheet date classified as trading. + References No definition available. + Details
Name: | wtm_TradingSecuritiesMaturitiesAfterOneThroughFiveYearsCostOrAmortizedCost
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the carrying value of securities which are expected to mature after one year and through five years from the balance sheet classified as trading. + References No definition available. + Details
Name: | wtm_TradingSecuritiesMaturitiesAfterOneThroughFiveYearsNetCarryingAmount
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents securities, at cost, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments, as defined), and fair value hedge accounting adjustments, if any, which are expected to mature after ten years from the balance sheet classified as trading. + References No definition available. + Details
Name: | wtm_TradingSecuritiesMaturitiesAfterTenYearsCostOrAmortizedCost
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the carrying value of debt securities which are expected to mature after ten years from the balance sheet date classified as trading. + References No definition available. + Details
Name: | wtm_TradingSecuritiesMaturitiesAfterTenYearsNetCarryingAmount
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents securities, at cost, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments, as defined), and fair value hedge accounting adjustments, if any, which are expected to mature within one year of the balance sheet date classified as trading. + References No definition available. + Details
Name: | wtm_TradingSecuritiesMaturitiesWithinOneYearCostOrAmortizedCost
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the carrying value of securities which are expected to mature within one year of the balance sheet date classified as trading. + References No definition available. + Details
Name: | wtm_TradingSecuritiesMaturitiesWithinOneYearNetCarryingAmount
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the cost or amortized cost of securities, categorized as trading securities, which do not have a single maturity date and which the Company has decided to disclose separately, rather than allocating such cost over several maturity groupings. + References No definition available. + Details
Name: | wtm_TradingSecuritiesMaturitiesWithoutSingleMaturityDateAmortizedCost
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the carrying value of securities, categorized as trading securities, which do not have a single maturity date and which the Company has decided to disclose separately, rather than allocating such cost over several maturity groupings. + References No definition available. + Details
Name: | wtm_TradingSecuritiesMaturitiesWithoutSingleMaturityDateCarryingValue
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_PreferredStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=wtm_FixedMaturitiesAndConvertibleFixedMaturitiesExcludingMortgageBackedSecuritesAssetBackedSecuritiesAndPreferredStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |