XML 19 R59.htm IDEA: XBRL DOCUMENT v3.19.3.a.u2

Investment Securities (Net Realized Investment Gain (losses) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investment securities
Net realized investment gains (losses), pre-tax		$ 96.6	$ (23.9)	$ 35.3
Net realized investment gains (losses), foreign, pre-tax		0.0	11.0	(11.2)
Net realized investment gains (losses), pre-tax, total		96.6	(12.9)	24.1
Income tax expense attributable to net realized investment gains (losses)		(10.6)	9.1	8.9
Income tax expense attributable to net realized investment gains (losses), foreign		0.0	0.0	0.0
Income tax expense attributable to net realized investment gains, total		(10.6)	9.1	8.9
Net realized investment gains (losses), after-tax		86.0	(14.8)	26.4
Net realized investment gains (losses), foreign, after-tax		0.0	11.0	(11.2)
Net realized investment gains (losses), total, after-tax		86.0	(3.8)	15.2
Realized gains		104.0	49.4	61.5
Realized losses		7.4	62.3	37.4
Fixed maturity investments
Investment securities
Net realized investment gains (losses), pre-tax		4.9	(29.8)	(1.6)
Net realized investment gains (losses), foreign, pre-tax		0.0	18.2	4.1
Net realized investment gains (losses), pre-tax, total		4.9	(11.6)	2.5
Short-term investments
Investment securities
Net realized investment gains (losses), pre-tax		0.2	(0.8)	(0.3)
Net realized investment gains (losses), foreign, pre-tax		0.0	0.0	0.0
Net realized investment gains (losses), pre-tax, total		0.2	(0.8)	(0.3)
Common equity securities
Investment securities
Net realized investment gains (losses), pre-tax		85.9	6.6	18.1
Net realized investment gains (losses), foreign, pre-tax		0.0	0.0	6.0
Net realized investment gains (losses), pre-tax, total		85.9	6.6	24.1
Other long-term investments
Investment securities
Net realized investment gains (losses), pre-tax		5.6	0.1	19.1
Net realized investment gains (losses), foreign, pre-tax		0.0	(7.2)	(21.3)
Net realized investment gains (losses), pre-tax, total		5.6	$ (7.1)	$ (2.2)
MediaAlpha
Investment securities
Realized gain from transaction	$ 67.5	$ 67.5

X

- Definition

Amount before tax of foreign currency transaction realized gain (loss) recognized in the income statement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=109240200&loc=d3e30690-110894

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6450222&loc=d3e30840-110895

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 830
-SubTopic 20
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109240200&loc=d3e30700-110894

+ Details

Name:	us-gaap_ForeignCurrencyTransactionGainLossRealized
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_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems
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

No definition available.

+ Details

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

X

- Definition

Amount of gain (loss) realized from securities classified as trading.

+ References

No definition available.

+ Details

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

X

- Definition

This item represents the loss realized during the period from the sale of trading securities.

+ References

No definition available.

+ Details

Name:	us-gaap_TradingSecuritiesRealizedLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax

+ References

No definition available.

+ Details

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

X

- Definition

Realized Gain From Transaction

+ References

No definition available.

+ Details

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

X

- Definition

Tax on Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities

+ References

No definition available.

+ Details

Name:	wtm_TaxonNetRealizedGainLossandForeignCurrencyGainLossonTradingSecurities
Namespace Prefix:	wtm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Trading Securities, Realized Foreign Currency Gain (Loss) Net of Tax

+ References

No definition available.

+ Details

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

X

- Definition

Trading Securities, Realized Gain (Loss), Total

+ References

No definition available.

+ Details

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

X

- Definition

Trading Securities Realized Holding Gain (Loss) on Investments after Tax

+ References

No definition available.

+ Details

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

X

- Definition

Trading Securities, Tax on Realized Foreign Currency Transaction Gain (Loss) Tax

+ References

No definition available.

+ Details

Name:	wtm_TradingSecuritiesTaxonRealizedForeignCurrencyTransactionGainLossTax
Namespace Prefix:	wtm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Trading securities, Tax on Realized Holding Gain (Loss) on Investments

+ References

No definition available.

+ Details

Name:	wtm_TradingsecuritiesTaxonRealizedHoldingGainLossonInvestments
Namespace Prefix:	wtm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_FixedMaturitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ShortTermInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_OtherLongTermInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	dei_LegalEntityAxis=wtm_MediaAlphaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: