XML 173 R153.htm IDEA: XBRL DOCUMENT
v3.6.0.2

Investments in Unconsolidated Affiliates (Symetra Narrative) (Details) - USD ($) | 3 Months Ended | 9 Months Ended | 10 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | ---
Mar. 31, 2016 | Dec. 31, 2015 | Sep. 30, 2016 | Sep. 30, 2015 | Nov. 05, 2015 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014 | Feb. 01, 2016 | Dec. 31, 2011
Investments in unconsolidated affiliates |  |  |  |  |  |  |  |  |  |
Trading Securities, Change in Unrealized Holding Gain (Loss) |  |  |  |  |  | $ (267,300,000) | $ 152,900,000 | $ (79,300,000) |  |
Trading Securities Unrealized Holding Gain (Loss) on Investments after Tax |  |  |  |  |  | (226,600,000) | 140,600,000 | (69,400,000) |  |
Realized gains |  |  |  |  |  | 315,500,000 | 112,900,000 | 194,000,000 |  |
After tax amortization through equity in net unrealized losses |  |  |  |  |  | 0 | (36,300,000) | 75,300,000 |  |
Sales of common equity securities |  |  |  |  |  | $ 1,200,800,000 | $ 461,400,000 | 609,800,000 |  |
Common shares, par value per share (in dollars per share) |  | $ 1.00 |  |  |  | $ 1.00 | $ 1.00 |  |  |
Symetra |  |  |  |  |  |  |  |  |  |
Investments in unconsolidated affiliates |  |  |  |  |  |  |  |  |  |
Payments to Acquire Interest in Subsidiaries and Affiliates |  |  |  |  |  |  |  | 195,000,000 |  |
Trading Securities, Change in Unrealized Holding Gain (Loss) |  | $ 258,800,000 |  |  |  |  |  |  |  |
Trading Securities Unrealized Holding Gain (Loss) on Investments after Tax |  | $ 241,100,000 |  |  |  |  |  |  |  |
Realized gains | $ 4,700,000 |  |  |  |  |  |  |  |  |
Shares of symetra financial corporation owned (in shares) |  |  |  |  | 20,562,379 |  |  |  |  |
Ownership interest (as a percent) |  |  |  |  | 17.70% |  |  |  |  |
Fair value of investment |  |  |  |  |  |  |  |  |  | $ 261,000,000
Estimated fair value of investment per share |  |  |  |  |  |  |  |  |  | $ 15
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity |  |  |  |  | $ 159,900,000 |  |  |  |  |
Term of amortization (in years) |  |  | 30 years |  |  |  |  |  |  |
Dividends Payable, Amount Per Share |  |  |  |  |  |  |  |  | $ 32.00 |
Common Stock | Symetra |  |  |  |  |  |  |  |  |  |
Investments in unconsolidated affiliates |  |  |  |  |  |  |  |  |  |
Dividends received |  |  |  |  | $ (16,900,000) |  |  |  |  |
Per share price, class of warrant (in dollars per share) |  |  |  |  | $ 31.67 |  |  |  |  |
equity in earnings of unconsolidated affiliates [Member] | Symetra |  |  |  |  |  |  |  |  |  |
Investments in unconsolidated affiliates |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity |  |  |  |  | $ 32,600,000 |  |  |  |  |
After tax amortization through equity in earnings |  |  |  | $ 2,200,000 |  |  |  | 2,800,000 |  |
Net unrealized gains (losses) of unconsolidated affiliates [Member] | Symetra |  |  |  |  |  |  |  |  |  |
Investments in unconsolidated affiliates |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity |  |  |  |  | $ 127,300,000 |  |  |  |  |
After tax amortization through equity in net unrealized losses |  |  |  | $ 8,900,000 |  |  |  | $ 11,700,000 |  |
Symetra |  |  |  |  |  |  |  |  |  |
Investments in unconsolidated affiliates |  |  |  |  |  |  |  |  |  |
Sales of common equity securities | $ 658,000,000 |  |  |  |  |  |  |  |  |

X
- Definition Face amount or stated value per share of common stock. + 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(29)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_CommonStockParOrStatedValuePerShare
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition The per share amount of a dividend declared, but not paid, as of the financial reporting date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586 + Details
Name: | us-gaap_DividendsPayableAmountPerShare
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition Difference between amount at which an investment accounted for under the equity method of accounting is carried (reported) on the balance sheet and amount of underlying equity in net assets the reporting Entity has in the investee. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571 + Details
Name: | us-gaap_EquityMethodInvestmentDifferenceBetweenCarryingAmountAndUnderlyingEquity
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents disclosure of the amount of dividends or other distributions received from unconsolidated subsidiaries, certain corporate joint ventures, and certain noncontrolled corporation; these investments are accounted for under the equity method of accounting. This element excludes distributions that constitute a return of investment, which are classified as investing activities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(10)) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(12)) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 + Details
Name: | us-gaap_EquityMethodInvestmentDividendsOrDistributions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571 + Details
Name: | us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Fair value portion of investments accounted under the equity method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 25 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=66022186&loc=d3e32014-111567 + Details
Name: | us-gaap_EquityMethodInvestmentsFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Number of shares of affiliates held for management investment companies. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 6 -Subparagraph (SX 210.12-14.Column B) -URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611322-123010 + Details
Name: | us-gaap_InvestmentsInAndAdvancesToAffiliatesBalanceShares
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition The cash outflow associated with the acquisition of or advances to an entity that is related to it but not strictly controlled (for example, an unconsolidated subsidiary, affiliate, and joint venture or equity method investment) or the acquisition of an additional interest in a subsidiary (controlled entity). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3213-108585 + Details
Name: | us-gaap_PaymentsToAcquireInterestInSubsidiariesAndAffiliates
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Price of a single share of a number of saleable stocks of a company. + References No definition available. + Details
Name: | us-gaap_SharePrice
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

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

X
- Definition This item represents the gain realized during the period from the sale of trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27357-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.7(c)) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 Reference 3: 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_TradingSecuritiesRealizedGain
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of unrealized holding gain (loss) recognized in the income statement for 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 -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.7(c)) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 35 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=27723805&loc=d3e24584-111560 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27357-111563 + Details
Name: | us-gaap_TradingSecuritiesUnrealizedHoldingGainLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Represents the period over which basis difference amortized. + References No definition available. + Details
Name: | wtm_AmortizationPeriodOfBasisDifference
Namespace Prefix: | wtm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents fair value per share of investments accounted for under the equity method of accounting as of the balance sheet date. + References No definition available. + Details
Name: | wtm_EquityMethodInvestmentsFairValuePerShare
Namespace Prefix: | wtm_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents recognized after tax amortization through equity in earnings of unconsolidated affiliates. + References No definition available. + Details
Name: | wtm_InvestmentsInUnconsolidatedAffiliatesAmortizationThroughEquityInEarningsAfterTax
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Represents recognized after tax amortization through equity in net unrealized losses from investments in unconsolidated affiliates. + References No definition available. + Details
Name: | wtm_InvestmentsInUnconsolidatedAffiliatesAmortizationThroughEquityInNetUnrealizedLossesAfterTax
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The cash inflow associated with the sale of equity securities classified as trading. + References No definition available. + Details
Name: | wtm_ProceedsFromSaleOfTradingCommonEquitySecurities
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Represents the net unrealized investment gains (losses) after income taxes. + References No definition available. + Details
Name: | wtm_TradingSecuritiesUnrealizedHoldingGainLossonInvestmentsafterTax
Namespace Prefix: | wtm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_InvestmentsInAndAdvancesToAffiliatesCategorizationAxis=wtm_SymetraMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_CommonStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementEquityComponentsAxis=wtm_EquityinearningsofunconsolidatedaffiliatesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementEquityComponentsAxis=wtm_NetunrealizedgainslossesofunconsolidatedaffiliatesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentAxis=wtm_SymetraMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |