Acquisition (Details) (USD $)			0 Months Ended
Dec. 31, 2012 White Mountains Holdings (Luxembourg)	Oct. 07, 2011 White Mountains Holdings (Luxembourg)	Oct. 07, 2011 Answer Financial Inc. item
Recorded amount of assets acquired
Cash paid on business acquisition		$ 1,010,000,000
Number of insurance companies for which comparison quotes for auto and homeowners insurance are offered			20
Recorded amount in connection with the acquisition
Present value of future profits		42,000,000
Goodwill		368,000,000
Other intangible assets		426,000,000
Reserve for property-liability claims and claims expense	2,000,000	487,000,000
Unearned premiums		$ 229,000,000

The amount of acquisition cost of a business combination allocated to other intangible assets.

No definition available.

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- Definition

The amount of acquisition cost of a business combination allocated to reserve for property-liability claims and claims expense.

+ References

No definition available.

+ Details

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- Definition

The amount of acquisition cost of a business combination allocated to other unearned premiums.

+ References

No definition available.

+ Details

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- Definition

The amount of acquisition cost of a business combination allocated to value of business acquired (also called present value of future profits).

+ References

No definition available.

+ Details

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- Definition

Represents the number of insurance companies for which comparison quotes for auto and homeowners insurance are offered by the entity.

+ References

No definition available.

+ Details

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- Definition

Amount of cash paid to acquire the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141R

-Paragraph 68

-Subparagraph f(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 Statement of Financial Accounting Standard (FAS)

-Number 141

-Paragraph 51

-Subparagraph d

-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.

+ Details

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- Definition

Amount of goodwill arising from a business combination, which is the excess of the cost of the acquired entity over the amounts assigned to assets acquired and liabilities assumed.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141

-Paragraph 52

-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 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 141

-Paragraph 53

-Subparagraph d

-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.

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