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Investment Securities (Fair Value Measurement by Level) (Details) (USD $) | 6 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Jun. 30, 2013 | Jun. 30, 2012 | Dec. 31, 2012 | Dec. 31, 2011
Investment securities |  |  |  |  |  |  |  |
Fixed maturity investments reclassified to assets held for sale |  |  |  |  | $ 338,100,000 |  |  |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 | 8.0 |  | 21.0 |  |  |  |  |
Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 6,565,500,000 | [1],[2] | 6,571,900,000 | [3],[4] | 6,950,700,000 | [1],[2] | 7,500,800,000 | [3],[4]
Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 1,420,600,000 | [5] | 1,151,500,000 | [6] | 1,355,100,000 | [5] | 1,033,100,000 | [6]
Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 4,721,200,000 |  | 5,006,400,000 |  | 5,206,100,000 |  | 6,088,200,000 |
Debt securities issued by corporations |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 2,314,800,000 | [7] |  |  | 2,385,100,000 | [7] |  |
Mortgage-backed and asset-backed securities | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 1,834,600,000 |  |  |  | 2,095,600,000 |  |  |
Mortgage-backed and asset-backed securities | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 1,788,600,000 |  |  |  | 2,073,500,000 |  |  |
Mortgage-backed and asset-backed securities | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 46,000,000 |  |  |  | 22,100,000 |  |  |
Fixed maturity investments. | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 116,900,000 |  | 119,700,000 |  | 92,900,000 |  | 78,900,000 |
Common equity securities | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 37,600,000 |  | 35,800,000 |  | 37,300,000 |  | 32,300,000 |
Convertible fixed maturity investments | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  | 0 |  | 0 |  | 0 |
Other long-term investments | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 269,200,000 |  | 258,500,000 | [4] | 259,300,000 |  | 268,300,000 | [3],[4]
Fair value measured on a recurring basis | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 7,172,300,000 |  |  |  | 7,581,300,000 |  |  |
Fair value measured on a recurring basis | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 2,002,700,000 |  |  |  | 1,985,700,000 |  |  |
Fair value measured on a recurring basis | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 4,745,900,000 |  |  |  | 5,206,100,000 |  |  |
Fair value measured on a recurring basis | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 423,700,000 |  |  |  | 389,500,000 |  |  |
Fair value measured on a recurring basis | U.S. Government and agency obligations | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 512,300,000 |  |  |  | 440,100,000 |  |  |
Fair value measured on a recurring basis | U.S. Government and agency obligations | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 445,500,000 |  |  |  | 369,100,000 |  |  |
Fair value measured on a recurring basis | U.S. Government and agency obligations | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 66,800,000 |  |  |  | 71,000,000 |  |  |
Fair value measured on a recurring basis | U.S. Government and agency obligations | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 2,314,800,000 |  |  |  | 2,385,100,000 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 1,000,000 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 2,314,800,000 |  |  |  | 2,384,100,000 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 705,400,000 |  |  |  | 727,100,000 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 705,400,000 |  |  |  | 727,100,000 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 268,400,000 |  |  |  | 330,800,000 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 268,400,000 |  |  |  | 330,800,000 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 393,400,000 |  |  |  | 401,400,000 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 1,000,000 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 393,400,000 |  |  |  | 400,400,000 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 287,400,000 |  |  |  | 276,100,000 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 287,400,000 |  |  |  | 276,100,000 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Basic materials | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 157,900,000 |  |  |  | 189,100,000 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Basic materials | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Basic materials | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 157,900,000 |  |  |  | 189,100,000 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Basic materials | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 213,500,000 |  |  |  | 181,500,000 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 213,500,000 |  |  |  | 181,500,000 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 188,700,000 |  |  |  | 204,200,000 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 188,700,000 |  |  |  | 204,200,000 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 88,200,000 |  |  |  | 54,000,000 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 88,200,000 |  |  |  | 54,000,000 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Other: | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 11,900,000 |  |  |  | 20,900,000 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Other: | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Other: | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 11,900,000 |  |  |  | 20,900,000 |  |  |
Fair value measured on a recurring basis | Debt securities issued by corporations | Other: | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Municipal obligations | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 5,000,000 |  |  |  | 5,200,000 |  |  |
Fair value measured on a recurring basis | Municipal obligations | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Municipal obligations | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 5,000,000 |  |  |  | 5,200,000 |  |  |
Fair value measured on a recurring basis | Municipal obligations | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 1,834,600,000 |  |  |  | 2,095,600,000 |  |  |
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 1,788,600,000 |  |  |  | 2,073,500,000 |  |  |
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 46,000,000 |  |  |  | 22,100,000 |  |  |
Fair value measured on a recurring basis | Foreign government, agency and provincial obligations | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 439,700,000 |  |  |  | 521,900,000 |  |  |
Fair value measured on a recurring basis | Foreign government, agency and provincial obligations | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 46,700,000 |  |  |  | 52,100,000 |  |  |
Fair value measured on a recurring basis | Foreign government, agency and provincial obligations | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 393,000,000 |  |  |  | 469,800,000 |  |  |
Fair value measured on a recurring basis | Foreign government, agency and provincial obligations | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Non-cumulative perpetual preference shares | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 86,300,000 |  |  |  | 86,400,000 |  |  |
Fair value measured on a recurring basis | Non-cumulative perpetual preference shares | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Non-cumulative perpetual preference shares | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 15,400,000 |  |  |  | 15,600,000 |  |  |
Fair value measured on a recurring basis | Non-cumulative perpetual preference shares | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 70,900,000 |  |  |  | 70,800,000 |  |  |
Fair value measured on a recurring basis | Fixed maturity investments. | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 5,192,700,000 | [1] |  |  | 5,534,300,000 | [8] |  |
Fair value measured on a recurring basis | Fixed maturity investments. | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 492,200,000 | [1] |  |  | 422,200,000 | [8] |  |
Fair value measured on a recurring basis | Fixed maturity investments. | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 4,583,600,000 | [1] |  |  | 5,019,200,000 | [8] |  |
Fair value measured on a recurring basis | Fixed maturity investments. | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 116,900,000 | [1] |  |  | 92,900,000 | [8] |  |
Fair value measured on a recurring basis | Short-term investments | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 606,800,000 |  |  |  | 630,600,000 |  |  |
Fair value measured on a recurring basis | Short-term investments | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 582,100,000 |  |  |  | 630,600,000 |  |  |
Carrying value of investment accounted for using the equity method | 606,800,000 |  | 618,400,000 |  | 630,600,000 |  | 846,000,000 |
Realized and unrealized gain | 0 |  | 500,000 |  | 100,000 |  |  |
Fair value measured on a recurring basis | Short-term investments | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 24,700,000 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Short-term investments | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Common equity securities | Consumer | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 289,400,000 |  |  |  | 255,600,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Consumer | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 289,400,000 |  |  |  | 255,600,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Consumer | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Common equity securities | Consumer | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Common equity securities | Industrial | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 69,100,000 |  |  |  | 41,900,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Industrial | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 69,100,000 |  |  |  | 41,900,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Industrial | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Common equity securities | Industrial | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Common equity securities | Financials | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 301,100,000 |  |  |  | 324,500,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Financials | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 263,500,000 |  |  |  | 286,300,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Financials | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 900,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Financials | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 37,600,000 |  |  |  | 37,300,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Communications | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 45,700,000 |  |  |  | 35,200,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Communications | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 45,700,000 |  |  |  | 35,200,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Communications | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Common equity securities | Communications | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Common equity securities | Basic materials | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 62,200,000 |  |  |  | 103,300,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Basic materials | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 62,200,000 |  |  |  | 103,300,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Basic materials | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Common equity securities | Basic materials | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Common equity securities | Energy | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 75,700,000 |  |  |  | 101,000,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Energy | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 75,700,000 |  |  |  | 101,000,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Energy | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Common equity securities | Energy | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Common equity securities | Utilities | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 36,700,000 |  |  |  | 43,600,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Utilities | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 36,500,000 |  |  |  | 43,400,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Utilities | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 200,000 |  |  |  | 200,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Utilities | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Common equity securities | Technology | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 72,700,000 |  |  |  | 55,000,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Technology | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 72,700,000 |  |  |  | 55,000,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Technology | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Common equity securities | Technology | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Common equity securities | Other: | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 76,900,000 |  |  |  | 69,600,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Other: | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 13,600,000 |  |  |  | 11,200,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Other: | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 63,300,000 |  |  |  | 58,400,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Other: | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Common equity securities | Common equity securities | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 1,029,500,000 |  |  |  | 1,029,700,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Common equity securities | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 928,400,000 |  |  |  | 932,900,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Common equity securities | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 63,500,000 |  |  |  | 59,500,000 |  |  |
Fair value measured on a recurring basis | Common equity securities | Common equity securities | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 37,600,000 |  |  |  | 37,300,000 |  |  |
Fair value measured on a recurring basis | Convertible fixed maturity investments | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 74,100,000 |  |  |  | 127,400,000 |  |  |
Fair value measured on a recurring basis | Convertible fixed maturity investments | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Convertible fixed maturity investments | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 74,100,000 |  |  |  | 127,400,000 |  |  |
Fair value measured on a recurring basis | Convertible fixed maturity investments | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 |  |  |  | 0 |  |  |
Fair value measured on a recurring basis | Other long-term investments | Fair Value |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 269,200,000 | [2] |  |  | 259,300,000 | [9] |  |
Fair value measured on a recurring basis | Other long-term investments | Level 1 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 | [2] |  |  | 0 | [9] |  |
Fair value measured on a recurring basis | Other long-term investments | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 0 | [2] |  |  | 0 | [9] |  |
Fair value measured on a recurring basis | Other long-term investments | Level 3 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fair value investments | 269,200,000 | [2] |  |  | 259,300,000 | [9] |  |
Carrying value of investment accounted for using the equity method | 34,200,000 |  | 33,000,000 |  | 35,000,000 |  | 34,000,000 |
Fair value measured on a recurring basis | Forward Contracts | Level 2 Inputs |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Realized and unrealized (losses) gains | (100,000) |  |  |  | (100,000) |  |  |
Segment, Discontinued Operations |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Fixed maturity investments reclassified to assets held for sale | 260,800,000 |  | (111,800,000) |  | (338,100,000) |  |  |
Prospector Offshore Fund Ltd [Member] | Fair value measured on a recurring basis | Short-term investments |  |  |  |  |  |  |  |
Investment securities |  |  |  |  |  |  |  |
Realized and unrealized gain | $ 0 |  | $ 0 |  |  |  |  |
[1] | Carrying value includes $260.8 that is classified as assets held for sale relating to discontinued operations.
[2] | Excludes carrying value of $34.2 associated with other long-term investment limited partnerships accounted for using the equity method and $(0.1) related to forward contracts.
[3] | Carrying value includes $111.8 that is classified as assets held for sale relating to discontinued operations.
[4] | Excludes carrying value of $33.0 and $34.0 at January 1, 2012 and June 30, 2012 associated with other long-term investment limited partnerships accounted for using the equity method.
[5] | Excludes carrying value of $630.6 and $606.8 at January 1, 2013 and June 30, 2013 and realized and unrealized gain for the periods of $0.1 and $0.8 associated with short-term investments classified.
[6] | Excludes carrying value of $846.0 and $618.4 January 1, 2012 and June 30, 2012 realized and unrealized loss for the period of $0.5 associated with short-term investment
[7] | Credit ratings are assigned based on the following hierarchy: 1) Standard and Poor's Financial Services LLC ("Standard & Poor’s") and 2) Moody’s Investor Service ("Moody's").
[8] | Carrying value includes $338.1 that is classified as assets held for sale relating to discontinued operations.
[9] | Excludes carrying value of $35.0 associated with other long-term investment limited partnerships accounted for using the equity method and $(0.1) related to currency forward contracts.

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- Definition This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents investment securities as of the balance sheet date which may include marketable securities, derivative financial instruments, and investments accounted for under the equity method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 13 -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 Accounting Standards Codification -Glossary Available-for-Sale Securities -URI http://asc.fasb.org/extlink&oid=6505594 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 12 -Subparagraph a -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 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=7534914&loc=d3e22054-111558 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Subparagraph a, f, g -Article 7 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 35 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=16383099&loc=d3e24584-111560 + Details
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