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Derivatives Additional Collateral (Details) (White Mountains Life Re, USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Credit risk on derivative instruments
Collateral cash and investments	$ 229.8	$ 393.6	$ 390.9
Cash
Credit risk on derivative instruments
Derivative collateral right to reclaim	188.5	249.8	360.1
Short-term investments
Credit risk on derivative instruments
Derivative collateral right to reclaim	15.6	5.1	1.5
Fixed maturity investments.
Credit risk on derivative instruments
Derivative collateral right to reclaim	$ 25.7	$ 138.7	$ 29.3

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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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