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Derivatives (Variable Annuity Reinsurance Liabilities and Derivative Instruments (Details) (White Mountains Life Re, USD $) In Millions, unless otherwise specified | 3 Months Ended |
--- | --- | ---
Mar. 31, 2013 | Mar. 31, 2012 | Dec. 31, 2012
Variable Annuity Reinsurance [Line Items] |  |  |  |  |
Change in fair value of variable annuity death benefit liabilities, included in other general and administrative expenses | $ 5.6 |  | $ 8.8 |  |
Changes in derivative instruments |  |  |  |  |
Beginning balance | 98.3 |  |  |  |
Realized and unrealized gains (losses) | 181.8 |  | 206.5 |  |
Ending balance | 75.8 |  |  |  |
Collateral cash and investments | 229.8 |  | 390.9 |  | 393.6
Fair Value |  |  |  |  |
Changes in derivative instruments |  |  |  |  |
Beginning balance | 98.3 |  | 290.4 |  |
Purchases | 36.1 |  | 6.1 |  |
Realized and unrealized gains (losses) | (181.8) |  | (206.5) |  |
Transfers in | 0 |  | 0 |  |
Sales/settlements | 123.2 |  | 84.3 |  |
Ending balance | 75.8 |  | 174.3 |  |
Level 3 Inputs |  |  |  |  |
Changes in variable annuity liabilities |  |  |  |  |
Beginning balance | (441.5) |  | (768.5) |  |
Purchases | 0 |  | 0 |  |
Realized and unrealized gains (losses) | 189.9 | [1] | 220.0 | [1] |
Transfers in | 0 |  | 0 |  |
Sales/settlements |  |  | 0 |  |
Ending balance | (251.6) |  | (548.5) |  |
Changes in derivative instruments |  |  |  |  |
Beginning balance | 140.5 | [2] | 247.1 | [2] |
Purchases | 36.1 | [2] | 6.1 | [2] |
Realized and unrealized gains (losses) | (49.2) | [2] | (60.3) | [2] |
Transfers in | 0 | [2] | 0 | [2] |
Sales/settlements |  | [2] | (9.1) | [2] |
Ending balance | 127.4 | [2] | 183.8 | [2] |
Level 2 Inputs |  |  |  |  |
Changes in derivative instruments |  |  |  |  |
Beginning balance | (20.5) | [2],[3] | 39.2 | [2],[3] |
Purchases | 0 | [2],[3] | 0 | [2],[3] |
Realized and unrealized gains (losses) | (85.5) | [2],[3] | (98.2) | [2],[3] |
Transfers in | 0 | [2],[3] | 0 | [2],[3] |
Sales/settlements | 63.1 | [2],[3] | 58.9 | [2],[3] |
Ending balance | (42.9) | [2],[3] | (0.1) | [2],[3] |
Level 1 Inputs |  |  |  |  |
Changes in derivative instruments |  |  |  |  |
Beginning balance | (21.7) | [4] | 4.1 | [4] |
Purchases | 0 | [4] | 0 | [4] |
Realized and unrealized gains (losses) | (47.1) | [4] | (48.0) | [4] |
Transfers in | 0 | [4] | 0 | [4] |
Sales/settlements | 60.1 | [4] | 34.5 | [4] |
Ending balance | $ (8.7) | [4] | $ (9.4) | [4] |
[1] | Includes $5.6 and $8.8 for the three months ended March 31, 2013 and 2012, respectively, related to the increase in the fair value of variable annuity death benefit liabilities, which are included in other general and administrative expenses.
[2] | Consists of over-the-counter instruments.
[3] | Consists of interest rate swaps, total return swaps, foreign currency forward contracts, and bond forwards. Fair value measurement based upon bid/ask pricing quotes for similar instruments that are actively traded, where available. Swaps for which an active market does not exist have been priced using observable inputs including the swap curve and the underlying bond index.
[4] | Consists of exchange traded equity index, foreign currency and interest rate futures. Fair value measurements based upon quoted prices for identical instruments that are actively traded.

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- Definition Amount of gain (loss) recognized in earnings, arising from liabilities measured at fair value on a recurring basis using unobservable inputs (level 3). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 157 -Paragraph 32 -Subparagraph c(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. + Details
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- Definition Purchases that have taken place during the period in relation to liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258 + Details
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