XML 109 R98.htm IDEA: XBRL DOCUMENT v3.21.1

Segment Information - Reconciliation of Revenue from Segments to Consolidated (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Revenues from contracts with customers	$ 83.6	$ 68.5
Other Revenue	94.6	(127.7)
Total revenues	178.2	(59.2)
HG Global/ BAM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
Other Revenue	(6.7)	17.5
Total revenues	(6.7)	17.5
Ark
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0
Other Revenue	109.1
Total revenues	109.1	0.0
NSM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	74.8	65.0
Other Revenue	0.0	0.0
Total revenues	74.8	65.0
Kudu
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
Other Revenue	24.1	(17.4)
Total revenues	24.1	(17.4)
Other Operations
Segment Reporting Information [Line Items]
Revenues from contracts with customers	8.8	3.5
Other Revenue	(31.9)	(127.8)
Total revenues	(23.1)	(124.3)
United Kingdom
Segment Reporting Information [Line Items]
Revenues from contracts with customers	13.1	10.0
United Kingdom | HG Global/ BAM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
United Kingdom | Ark
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0
United Kingdom | NSM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	13.1	10.0
United Kingdom | Kudu
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
United Kingdom | Other Operations
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
Specialty Transportation
Segment Reporting Information [Line Items]
Revenues from contracts with customers	20.7	20.3
Specialty Transportation | HG Global/ BAM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
Specialty Transportation | Ark
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0
Specialty Transportation | NSM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	20.7	20.3
Specialty Transportation | Kudu
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
Specialty Transportation | Other Operations
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
Real Estate
Segment Reporting Information [Line Items]
Revenues from contracts with customers	9.8	11.3
Real Estate | HG Global/ BAM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
Real Estate | Ark
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0
Real Estate | NSM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	9.8	11.3
Real Estate | Kudu
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
Real Estate | Other Operations
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
Social Services
Segment Reporting Information [Line Items]
Revenues from contracts with customers	6.7	6.3
Social Services | HG Global/ BAM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
Social Services | Ark
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0
Social Services | NSM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	6.7	6.3
Social Services | Kudu
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
Social Services | Other Operations
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
Pet
Segment Reporting Information [Line Items]
Revenues from contracts with customers	17.1	11.8
Pet | HG Global/ BAM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
Pet | Ark
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0
Pet | NSM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	17.1	11.8
Pet | Kudu
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
Pet | Other Operations
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
Other
Segment Reporting Information [Line Items]
Revenues from contracts with customers	9.7	6.7
Other | HG Global/ BAM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
Other | Ark
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0
Other | NSM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	7.4	5.3
Other | Kudu
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
Other | Other Operations
Segment Reporting Information [Line Items]
Revenues from contracts with customers	2.3	1.4
Total commission and other revenue
Segment Reporting Information [Line Items]
Revenues from contracts with customers	77.1	66.4
Total commission and other revenue | HG Global/ BAM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
Total commission and other revenue | Ark
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0
Total commission and other revenue | NSM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	74.8	65.0
Total commission and other revenue | Kudu
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
Total commission and other revenue | Other Operations
Segment Reporting Information [Line Items]
Revenues from contracts with customers	2.3	1.4
Product revenues
Segment Reporting Information [Line Items]
Revenues from contracts with customers	6.5	2.1
Product revenues | HG Global/ BAM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
Product revenues | Ark
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0
Product revenues | NSM
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
Product revenues | Kudu
Segment Reporting Information [Line Items]
Revenues from contracts with customers	0.0	0.0
Product revenues | Other Operations
Segment Reporting Information [Line Items]
Revenues from contracts with customers	$ 6.5	$ 2.1

X

- Definition

Amount, including tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value-added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 41
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9038-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130545-203045

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8906-108599

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130543-203045

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 42
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9054-108599

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 40
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9031-108599

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 924
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 11.L)
-URI http://asc.fasb.org/extlink&oid=6472922&loc=d3e499488-122856

+ Details

Name:	us-gaap_RevenueFromContractWithCustomerIncludingAssessedTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 40
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9031-108599

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8906-108599

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 41
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9038-108599

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 42
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9054-108599

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(g)(1)(ii))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 235
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-05(b)(2))
-URI http://asc.fasb.org/extlink&oid=120399901&loc=d3e537907-122884

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(1))
-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227

+ Details

Name:	us-gaap_Revenues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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_SegmentReportingInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Other Revenue

+ References

No definition available.

+ Details

Name:	wtm_OtherRevenue
Namespace Prefix:	wtm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=wtm_HgGlobalBamMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=wtm_ArkInsuranceHoldingsLimitedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=wtm_NSMInsuranceGroupMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=wtm_KuduInvestmentManagementLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=wtm_OtherEntityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_StatementGeographicalAxis=country_GB
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ProductOrServiceAxis=wtm_SpecialtyTransportationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ProductOrServiceAxis=us-gaap_RealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ProductOrServiceAxis=wtm_SocialServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ProductOrServiceAxis=wtm_PetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ProductOrServiceAxis=us-gaap_ServiceOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ProductOrServiceAxis=wtm_CommissionandOtherRevenueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ProductOrServiceAxis=us-gaap_ProductMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: