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Derivatives (Additional Collateral) (Details) (White Mountains Life Re, USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Credit risk on derivative instruments
Derivative Collateral Right to Reclaim	$ 30.6	$ 73.2
Collateral Cash and Investments	393.6	485.3
Cash
Credit risk on derivative instruments
Derivative Collateral Right to Reclaim	249.8	453.5	326.0
Short-term investments
Credit risk on derivative instruments
Derivative Collateral Right to Reclaim	5.1	0.6
Fixed maturity investments
Credit risk on derivative instruments
Derivative Collateral Right to Reclaim	$ 138.7	$ 31.2

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- Details

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- Definition

Represents cash and short-term investments held and posted as collateral to reinsurance counterparties.

+ References

No definition available.

+ Details

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- Definition

The amount of collateral held against amounts due to counterparties for over the counter derivative instruments against net derivative instrument positions.

+ References

No definition available.

+ Details

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