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Investment Securities (Rollforward of Fair Value Measurements by Level) (Details) (USD $) | 12 Months Ended
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Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Investment securities |  |  |  |  |
Net realized and unrealized investment gains | $ 161,700,000 |  | $ 118,200,000 |  | $ 74,100,000
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Sales | (4,924,800,000) |  | (6,997,500,000) |  | (5,034,000,000)
Discontinued Operations |  |  |  |  |
Investment securities |  |  |  |  |
Net realized and unrealized investment gains | 0 |  | 0 |  | 700,000
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fixed maturity investments reclassified to assets held for sale (1) | (236,300,000) |  | (338,100,000) |  | (111,800,000)
Level 1 Inputs |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 1,355,100,000 |  | 1,033,100,000 |  |
Total realized and unrealized gains (losses) | 221,900,000 |  | 52,000,000 |  |
Foreign currency gains (losses) through OCI | (300,000) |  | 4,400,000 |  |
Amortization/Accretion | (1,000,000) |  | (800,000) |  |
Purchases | 862,100,000 |  | 1,216,900,000 |  |
Sales | (1,078,900,000) |  | (950,500,000) |  |
Net change in investments related to purchases and sales of consolidated/unconsolidated affiliates | 16,000,000 |  |  |  |
Transfers in | 1,800,000 |  | 0 |  |
Transfers out | 0 |  | 0 |  |
Fair value investments | 1,376,700,000 |  | 1,355,100,000 |  |
Level 1 Inputs | Fair value measured on a recurring basis |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 1,998,200,000 |  | 1,985,700,000 |  |
Level 1 Inputs | Fixed maturity investments | Fair value measured on a recurring basis |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 340,300,000 | [1] | 422,200,000 | [2] |
Level 1 Inputs | Convertible fixed maturity investments | Fair value measured on a recurring basis |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 0 |  | 0 |  |
Level 1 Inputs | Other long-term investments | Fair value measured on a recurring basis |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 0 | [3] | 0 | [4] |
Level 1 Inputs | Short-term investments | Fair value measured on a recurring basis |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 621,500,000 |  | 630,600,000 |  |
Level 2 Inputs |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 5,206,100,000 |  | 6,088,200,000 |  |
Total realized and unrealized gains (losses) | (56,900,000) |  | 53,600,000 |  |
Foreign currency gains (losses) through OCI | 12,500,000 |  | 81,900,000 |  |
Amortization/Accretion | (51,200,000) |  | (48,000,000) |  |
Purchases | 3,689,600,000 |  | 4,927,100,000 |  |
Sales | (3,842,800,000) |  | (5,937,000,000) |  |
Net change in investments related to purchases and sales of consolidated/unconsolidated affiliates | 2,700,000 |  |  |  |
Transfers in | 119,400,000 |  | 62,400,000 |  |
Transfers out | (97,200,000) |  | (22,100,000) |  |
Fair value investments | 4,982,200,000 |  | 5,206,100,000 |  |
Level 2 Inputs | Fair value measured on a recurring basis |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 4,996,600,000 |  | 5,206,100,000 |  |
Level 2 Inputs | Fixed maturity investments | Fair value measured on a recurring basis |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 4,833,500,000 | [1] | 5,019,200,000 | [2] |
Level 2 Inputs | Convertible fixed maturity investments | Fair value measured on a recurring basis |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 74,400,000 |  | 127,400,000 |  |
Level 2 Inputs | Other long-term investments | Fair value measured on a recurring basis |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 0 | [3] | 0 | [4] |
Level 2 Inputs | Forward contracts | Fair value measured on a recurring basis |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Change in fair value of derivatives, included in other revenue | (100,000) |  | 0 |  |
Level 2 Inputs | Short-term investments | Fair value measured on a recurring basis |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 14,400,000 |  | 0 |  |
Level 3 Inputs | Fair value measured on a recurring basis |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 407,600,000 |  | 389,500,000 |  |
Level 3 Inputs | Fixed maturity investments |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 92,900,000 |  | 78,900,000 |  |
Total realized and unrealized gains (losses) | (2,700,000) |  | 8,700,000 |  |
Foreign currency gains (losses) through OCI | 300,000 |  | 800,000 |  |
Amortization/Accretion | 0 |  | (800,000) |  |
Purchases | 37,900,000 |  | 144,400,000 |  |
Sales | (6,300,000) |  | (99,400,000) |  |
Net change in investments related to purchases and sales of consolidated/unconsolidated affiliates | 0 |  |  |  |
Transfers in | 90,300,000 |  | 22,100,000 |  |
Transfers out | (119,400,000) |  | (61,800,000) |  |
Fair value investments | 93,000,000 |  | 92,900,000 |  |
Number of investments | 3 |  |  |  |
Level 3 Inputs | Fixed maturity investments | Fair value measured on a recurring basis |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 93,000,000 | [1] | 92,900,000 | [2] |
Level 3 Inputs | Common equity securities |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 37,300,000 |  | 32,300,000 |  |
Total realized and unrealized gains (losses) | 1,000,000 |  | 12,400,000 |  |
Foreign currency gains (losses) through OCI | 0 |  | 200,000 |  |
Amortization/Accretion | 0 |  | 0 |  |
Purchases | 8,800,000 |  | 3,100,000 |  |
Sales | 0 |  | (10,100,000) |  |
Net change in investments related to purchases and sales of consolidated/unconsolidated affiliates | 0 |  |  |  |
Transfers in | 0 |  | 0 |  |
Transfers out | (1,000,000) |  | (600,000) |  |
Fair value investments | 46,100,000 |  | 37,300,000 |  |
Level 3 Inputs | Convertible fixed maturity investments |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 0 |  | 0.0 |  |
Total realized and unrealized gains (losses) | 0 |  | 0 |  |
Foreign currency gains (losses) through OCI | 0 |  | 0 |  |
Amortization/Accretion | 0 |  | 0 |  |
Purchases | 0 |  | 0 |  |
Sales | 0 |  | 0 |  |
Net change in investments related to purchases and sales of consolidated/unconsolidated affiliates | 0 |  |  |  |
Transfers in | 6,100,000 |  | 0 |  |
Transfers out | 0 |  | 0 |  |
Fair value investments | 6,100,000 |  | 0 |  |
Level 3 Inputs | Convertible fixed maturity investments | Fair value measured on a recurring basis |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 6,100,000 |  | 0 |  |
Level 3 Inputs | Other long-term investments |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 259,300,000 | [5],[6] | 268,300,000 | [5] |
Total realized and unrealized gains (losses) | 18,700,000 |  | (3,300,000) |  |
Foreign currency gains (losses) through OCI | (900,000) |  | 3,700,000 |  |
Amortization/Accretion | 0 |  | 0 |  |
Purchases | 37,100,000 |  | 39,400,000 |  |
Sales | (51,800,000) |  | (48,800,000) |  |
Net change in investments related to purchases and sales of consolidated/unconsolidated affiliates | 0 |  |  |  |
Transfers in | 0 |  | 0 |  |
Transfers out | 0 |  | 0 |  |
Fair value investments | 262,400,000 | [6] | 259,300,000 | [5],[6] |
Level 3 Inputs | Other long-term investments | Fair value measured on a recurring basis |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 262,400,000 | [3] | 259,300,000 | [4] |
Carrying value of investment accounted for using the equity method | 26,600,000 |  | 35,000,000 |  | 33,000,000
Level 3 Inputs | Short-term investments | Fair value measured on a recurring basis |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 0 |  | 0 |  |
Fair value |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 6,950,700,000 | [10],[5],[6],[7],[8],[9] | 7,500,800,000 | [5],[7],[8] |
Total realized and unrealized gains (losses) | 182,000,000 | [11] | 123,400,000 |  |
Foreign currency gains (losses) through OCI | 11,600,000 |  | 91,000,000 |  |
Amortization/Accretion | (52,200,000) |  | 49,600,000 |  |
Purchases | 4,635,500,000 |  | 6,330,900,000 |  |
Sales | (4,979,800,000) |  | 7,045,800,000 |  |
Net change in investments related to purchases and sales of consolidated/unconsolidated affiliates | 18,700,000 |  |  |  |
Transfers in | 217,600,000 |  | 84,500,000 |  |
Transfers out | (217,600,000) |  | 84,500,000 |  |
Fair value investments | 6,766,500,000 | [10],[6],[9] | 6,950,700,000 | [10],[5],[6],[7],[8],[9] |
Fair value | Fair value measured on a recurring basis |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 7,402,400,000 |  | 7,581,300,000 |  |
Fair value | Fixed maturity investments | Fair value measured on a recurring basis |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 5,266,800,000 | [1] | 5,534,300,000 | [2] |
Fair value | Convertible fixed maturity investments | Fair value measured on a recurring basis |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 80,500,000 |  | 127,400,000 |  |
Fair value | Other long-term investments | Fair value measured on a recurring basis |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 262,400,000 | [3] | 259,300,000 | [4] |
Fair value | Short-term investments | Fair value measured on a recurring basis |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Fair value investments | 635,900,000 |  | 630,600,000 |  | 0
Prospector |  |  |  |  |
Investment securities |  |  |  |  |
Net realized and unrealized investment gains | 0 |  |  |  |
Less than market price [Member] | Level 3 Inputs | Fixed maturity investments |  |  |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |  |  |
Transfers in | $ 1,300,000 |  |  |  |
[1] | Carrying value includes $236.3 that is classified as assets held for sale relating to discontinued operations.
[2] | Carrying value includes $338.1 that is classified as assets held for sale relating to discontinued operations.
[3] | Excludes carrying value of $26.6 associated with other long-term investment limited partnerships accounted for using the equity method and $(.1) related to currency forward contracts.
[4] | Excludes carrying value of $35.0 associated with other long-term investment limited partnerships accounted for using the equity method and $(.1) related to currency forward contracts.
[5] | Excludes carrying value of $35.0 and $33.0 at December 31, 2012 and January 1, 2012 associated with other long-term investment limited partnerships accounted for using the equity method and $(.1) at December 31, 2012 related to currency forward contracts.
[6] | Excludes carrying value of $26.6 and $35.0 at December 31, 2013 and January 1, 2013 associated with other long-term investments accounted for using the equity method and $(.1) at December 31, 2013 related to currency forward contracts.
[7] | Carrying value includes $338.1 and $111.8 at December 31, 2012 and January 1, 2012 that is classified as assets held for sale relating to AutoOne discontinued operations.
[8] | Excludes carrying value of $630.6 and $846.0 at December 31, 2012 and January 1, 2012 classified as short-term investments.
[9] | Excludes carrying value of $635.9 and $630.6 at December 31, 2013 and January 1, 2013 classified as short-term investments.
[10] | Carrying value includes $236.3 and $338.1 at December 31, 2013 and January 1, 2013 that is classified as assets held for sale relating to discontinued operations.
[11] | Excludes $20.6 of realized and unrealized losses associated with the Prospector Funds consolidation of investment-related liabilities and $.2 of realized and unrealized gains associated with short-term investments.

X
- Definition The sum of the periodic adjustments of the differences between securities' face values and purchase prices that are charged against earnings. This is called accretion if the security was purchased at a discount and amortization if it was purchased at premium. As a noncash item, this element is an adjustment to net income when calculating cash provided by or used in operations using the indirect method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
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- Definition Amount of increase (decrease) in the fair value of derivatives recognized in the income statement. + 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 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (a),(c),(d),(e) -URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624171-113959 + Details
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- Definition Fair value portion of investments accounted under the equity method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 25 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6903542&loc=d3e32014-111567 + Details
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- Definition This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting and losses recognized for other than temporary impairments (OTTI) of the subject investments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.7(c),9(a)) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27405-111563 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 7 -Article 5 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (c)-(e) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563 + Details
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- Definition Fair value portion of investment securities, including, but not limited to, 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 Accounting Standards Codification -Glossary Available-for-Sale Securities -URI http://asc.fasb.org/extlink&oid=6505594 Reference 2: 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 3: 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=28360136&loc=d3e22054-111558 Reference 4: 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 5: 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=27723805&loc=d3e24584-111560 + Details
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- Definition The cash outflow associated with the purchase of all investments (debt, security, other) during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3213-108585 + Details
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- Definition This element represents the amount of the total realized and unrealized (holding) gains or losses for the period which are included in the statement of income. + References No definition available. + Details
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- Definition Net change in investments related to purchases and sales of consolidated/unconsolidated affiliates + References No definition available. + Details
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