XML 103 R59.htm IDEA: XBRL DOCUMENT
v2.4.0.6

Significant Transactions (OneBeacon Runoff Business) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2012 | Sep. 30, 2012 | Jun. 30, 2012 | Mar. 31, 2012 | Dec. 31, 2011 | Sep. 30, 2011 | Jun. 30, 2011 | Mar. 31, 2011 | Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Significant Transactions |  |  |  |  |  |  |  |  |  |  |
Net loss from other discontinued operations | $ (0.5) | $ 106.8 | $ (0.5) | $ 9.2 | $ (647.6) | $ 30.1 | $ 2.4 | $ (6.5) | $ 24.0 | $ 36.7 | $ 30.1
OneBeacon Runoff |  |  |  |  |  |  |  |  |  |  |
Significant Transactions |  |  |  |  |  |  |  |  |  |  |
Gain (loss) on sale of discontinued operation, net of tax |  |  |  |  |  |  |  |  | (91.5) |  |
Loss attributable to change in discount rate | OneBeacon Runoff |  |  |  |  |  |  |  |  |  |  |
Significant Transactions |  |  |  |  |  |  |  |  |  |  |
Net loss from other discontinued operations |  |  |  |  |  |  |  |  | $ 9.0 |  |

X
- Definition Amount of gain (loss), after tax expense or benefit and not previously recognized, resulting from the sale of a business component. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 144 -Paragraph 47 -Subparagraph b -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6892542&loc=d3e957-107759 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 144 -Paragraph 43 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6360339&loc=d3e1361-107760 + Details
Name: | us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of income (loss) from a disposal group, net of income tax before extraordinary items allocable to noncontrolling interests. Includes, net of tax, income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 13 -Article 7 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6892542&loc=d3e957-107759 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 144 -Paragraph 47 -Subparagraph c -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 15 -Article 5 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 29 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.14) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 205 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6360339&loc=d3e1361-107760 Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 144 -Paragraph 43 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 9: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.12) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 + Details
Name: | us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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