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Derivatives (Variable Annuity Reinsurance Liabilities and Derivative Instruments (Details) (White Mountains Life Re [Member], USD $) In Millions, unless otherwise specified | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2012 | Sep. 30, 2011 | Sep. 30, 2012 | Sep. 30, 2011 | Dec. 31, 2011
Changes in variable annuity liabilities |  |  |  |  |  |  |  |  |
Derivative, Fair Value, Net |  |  |  |  | $ 290.4 |  |  |  |
Derivative, Gain (Loss) on Derivative, Net | (11.0) |  | 148.9 |  | (122.0) |  | 105.4 |  |
Derivative, Fair Value, Net | 242.1 |  |  |  | 242.1 |  |  |  |
Collateral Cash and Investments | 477.5 |  | 419.7 |  | 477.5 |  | 419.7 |  | 485.3
Fair Value |  |  |  |  |  |  |  |  |
Changes in variable annuity liabilities |  |  |  |  |  |  |  |  |
Derivative, Fair Value, Net | 250.3 |  | 269.0 | [1] | 290.4 |  | 347.5 | [1] |
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases | 0 |  | 0 | [1] | 6.1 |  | 5.0 | [1] |
Derivative, Gain (Loss) on Derivative, Net | (11.0) |  | 148.9 | [1] | (122.0) |  | 105.4 | [1] |
Fair Value Derivatives Measured on Recurring Basis, Asset Sales and Settlements | 2.8 |  | (64.1) | [1] | 67.6 |  | (104.1) | [1] |
Derivative, Fair Value, Net | 242.1 |  | 353.8 | [1] | 242.1 |  | 353.8 | [1] |
Level 3 Inputs |  |  |  |  |  |  |  |  |
Changes in derivative instruments |  |  |  |  |  |  |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value | (661.8) |  | (591.3) |  | (768.5) |  | (610.2) |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Purchases | 0 |  | 0 |  | 0 |  | 0 |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings | (10.6) |  | (170.0) |  | 96.1 |  | (151.1) |  |
Fair Value Measurement with Unobservable Inputs, Reconciliation, Recurring Basis, Liability Sales or Settlements | 0 |  | 0 |  | 0 |  | 0 |  |
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value | (672.4) |  | (761.3) |  | (672.4) |  | (761.3) |  |
Changes in variable annuity liabilities |  |  |  |  |  |  |  |  |
Derivative, Fair Value, Net | 213.0 | [2] | 232.7 | [2] | 247.1 | [2] | 275.3 | [2] |
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases | 0 | [2] | 0 | [2] | 6.1 | [2] | 5.0 | [2] |
Derivative, Gain (Loss) on Derivative, Net | 6.7 | [2] | 45.6 | [2] | (24.1) | [2] | 27.1 | [2] |
Fair Value Derivatives Measured on Recurring Basis, Asset Sales and Settlements | (6.7) | [2] | 0 | [2] | (16.1) | [2] | (29.1) | [2] |
Derivative, Fair Value, Net | 213.0 | [2] | 278.3 | [2] | 213.0 | [2] | 278.3 | [2] |
Level 2 Inputs |  |  |  |  |  |  |  |  |
Changes in variable annuity liabilities |  |  |  |  |  |  |  |  |
Derivative, Fair Value, Net | 61.0 | [2] | 48.2 | [2],[3] | 39.2 | [2] | 72.2 | [2],[3] |
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases | 0 | [2] | 0 | [2],[3] | 0 | [2] | 0 | [2],[3] |
Derivative, Gain (Loss) on Derivative, Net | (15.3) | [2] | 75.7 | [2],[3] | (71.8) | [2] | 67.5 | [2],[3] |
Fair Value Derivatives Measured on Recurring Basis, Asset Sales and Settlements | (12.5) | [2] | (48.4) | [2],[3] | 65.8 | [2] | (64.2) | [2],[3] |
Derivative, Fair Value, Net | 33.2 | [2] | 75.5 | [2],[3] | 33.2 | [2] | 75.5 | [2],[3] |
Level 1 Inputs |  |  |  |  |  |  |  |  |
Changes in variable annuity liabilities |  |  |  |  |  |  |  |  |
Derivative, Fair Value, Net | (23.7) |  | (11.9) | [4] | 4.1 |  | 0 | [4] |
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases | 0 |  | 0 | [4] | 0 |  | 0 | [4] |
Derivative, Gain (Loss) on Derivative, Net | (2.4) |  | 27.6 | [4] | (26.1) |  | 10.8 | [4] |
Fair Value Derivatives Measured on Recurring Basis, Asset Sales and Settlements | 22.0 |  | (15.7) | [4] | 17.9 |  | (10.8) | [4] |
Derivative, Fair Value, Net | $ (4.1) |  | $ 0 | [4] | $ (4.1) |  | $ 0 | [4] |
[1] | (4) In addition to derivative instruments, WM Life Re held cash, short-term and fixed maturity investments of $477.5 and $419.7 at September 30, 2012 and 2011 posted as collateral to its reinsurance counterparties.
[2] | (1) Consists of over-the-counter instruments.
[3] | (2) 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] | (3) 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 Fair value of the assets less the liabilities of a derivative or group of derivatives. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13433-108611 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13495-108611 + Details
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- Definition Net Increase or Decrease in the fair value of the derivative or group of derivatives included in earnings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5618551-113959 + Details
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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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- Definition This element represents a liability measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances. + 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) -URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258 + Details
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