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Investment Securities (Details 2) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
Net Realized and Unrealized Investment Gains and Losses |  |  |
Net realized investment gains (losses), pre-tax | $ 117.0 | $ 136.4 | $ (69.9)
Net unrealized gains (losses), pre-tax | (63.6) | 17.2 | 498.5
Net realized and unrealized investment gains (losses), pre-tax | 122.8 | 82.6 | 361.7
Income taxes attributable to realized and unrealized investment gains (losses) | (30.9) | (22.8) | (124.4)
Net realized and unrealized investment gains (losses), after-tax | 91.9 | 59.8 | 237.3
Net realized investment gains (losses) |  |  |
Net realized investment gains (losses), pre-tax | 117.0 | 136.4 | (69.9)
Income taxes attributable to realized investment gains (losses) | (37.0) | (42.1) | 14.9
Net realized investment gains (losses), after-tax | 80.0 | 94.3 | (55.0)
Gross realized investment gains recognized during the period | 191.6 | 205.0 | 157.3
Gross realized investment losses recognized during the period | 74.6 | 68.6 | 227.2
Accounts payable on unsettled investment purchases | 34.6 | 22.3 |
Accounts receivable on unsettled investment sales | 4.7 | 39.5 |
Net unrealized investment gains (losses) |  |  |
Net unrealized gains (losses), pre-tax | (63.6) | 17.2 | 498.5
Income taxes attributable to unrealized investment gains (losses) | 24.0 | 0.5 | (154.3)
Net unrealized investment gains (losses), after-tax | (39.6) | 17.7 | 344.2
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax | 69.4 | (71.0) | (66.9)
Income taxes attributable to unrealized investment gains, net foreign exchange gains (losses) | (17.9) | 18.8 | 15.0
Net unrealized investment gains (losses), net foreign currency gains (losses), after-tax | 51.5 | (52.2) | (51.9)
Net unrealized investment gains (losses) pre-tax, total changes in fair value reflected in earnings | 5.8 | (53.8) | 431.6
Income taxes attributable to unrealized investment gains (losses), total changes in fair value reflected in earnings | 6.1 | 19.3 | (139.3)
Net unrealized investment gains (losses) after-tax, total changes in fair value reflected in earnings | 11.9 | (34.5) | 292.3
Fixed maturity investments. |  |  |
Net Realized and Unrealized Investment Gains and Losses |  |  |
Net realized investment gains (losses), pre-tax | 49.4 | 96.9 | (7.4)
Net unrealized gains (losses), pre-tax | 7.6 | (67.4) | 333.9
Net realized investment gains (losses) |  |  |
Net realized investment gains (losses), pre-tax | 49.4 | 96.9 | (7.4)
Net unrealized investment gains (losses) |  |  |
Net unrealized gains (losses), pre-tax | 7.6 | (67.4) | 333.9
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax | 68.9 | (53.8) | (53.6)
Net unrealized investment gains (losses) pre-tax, total changes in fair value reflected in earnings | 76.5 | (121.2) | 280.3
Short-term investments |  |  |
Net Realized and Unrealized Investment Gains and Losses |  |  |
Net realized investment gains (losses), pre-tax |  |  | 0.2
Net unrealized gains (losses), pre-tax |  |  | (0.3)
Net realized investment gains (losses) |  |  |
Net realized investment gains (losses), pre-tax |  |  | 0.2
Net unrealized investment gains (losses) |  |  |
Net unrealized gains (losses), pre-tax |  |  | (0.3)
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax | (1.1) | 0.2 | 1.6
Net unrealized investment gains (losses) pre-tax, total changes in fair value reflected in earnings | (1.1) | 0.2 | 1.3
Common equity securities |  |  |
Net Realized and Unrealized Investment Gains and Losses |  |  |
Net realized investment gains (losses), pre-tax | 34.6 | 6.9 | (46.4)
Net unrealized gains (losses), pre-tax | (40.6) | 72.4 | 57.9
Net realized investment gains (losses) |  |  |
Net realized investment gains (losses), pre-tax | 34.6 | 6.9 | (46.4)
Net unrealized investment gains (losses) |  |  |
Net unrealized gains (losses), pre-tax | (40.6) | 72.4 | 57.9
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax | (1.8) | (9.6) | (9.9)
Net unrealized investment gains (losses) pre-tax, total changes in fair value reflected in earnings | (42.4) | 62.8 | 48.0
Convertible fixed maturities |  |  |
Net Realized and Unrealized Investment Gains and Losses |  |  |
Net realized investment gains (losses), pre-tax | (2.2) | 16.7 | 15.6
Net unrealized gains (losses), pre-tax | (11.5) | (5.4) | 39.8
Net realized investment gains (losses) |  |  |
Net realized investment gains (losses), pre-tax | (2.2) | 16.7 | 15.6
Net unrealized investment gains (losses) |  |  |
Net unrealized gains (losses), pre-tax | (11.5) | (5.4) | 39.8
Net unrealized investment gains (losses) pre-tax, total changes in fair value reflected in earnings | (11.5) | (5.4) | 39.8
Other long-term investments |  |  |
Net Realized and Unrealized Investment Gains and Losses |  |  |
Net realized investment gains (losses), pre-tax | 35.2 | 15.9 | (31.9)
Net unrealized gains (losses), pre-tax | (19.1) | 17.6 | 67.2
Net realized investment gains (losses) |  |  |
Net realized investment gains (losses), pre-tax | 35.2 | 15.9 | (31.9)
Net unrealized investment gains (losses) |  |  |
Net unrealized gains (losses), pre-tax | (19.1) | 17.6 | 67.2
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax | 3.4 | (7.8) | (5.0)
Net unrealized investment gains (losses) pre-tax, total changes in fair value reflected in earnings | $ (15.7) | $ 9.8 | $ 62.2

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- Definition The sum of the realized and unrealized net gain (loss) on trading securities during the period. + References Reference 1: 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 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 + Details
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- Definition Aggregate amounts payable to broker-dealers and clearing organizations include amounts payable for securities failed to receive, certain deposits received for securities loaned, amounts payable to clearing organizations on open transactions, and floor-brokerage payables. In addition, the net receivable or payable arising from unsettled trades would be reflected in those captions. A broker-dealer that purchases securities, either for its own account or for a customer's account, but does not receive the securities on the settlement date records the amount of money representing the purchase price of the securities, including any accrued interest, as a liability to the selling broker-dealer. This liability is paid when the securities are received by the purchasing broker-dealer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Audit and Accounting Guide (AAG) -Number AAG-BRD -Chapter 4 -Paragraph 80 -Subparagraph Exhibit 4-8, 4 -IssueDate 2006-05-01 -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 AICPA -Name Audit and Accounting Guide (AAG) -Number AAG-BRD -Chapter 4 -Paragraph 24-31, 35 -IssueDate 2006-05-01 -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 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Audit and Accounting Guide (AAG) -Number AAG-BRD -Chapter 7 -Paragraph 24, 25 -IssueDate 2006-05-01 -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 Amount receivable from securities failed to deliver, certain deposits for securities borrowed, open transactions, good faith and margin deposits, commissions and floor brokerage items. Also cash and securities [guarantee] on deposit with [commodities] clearing organizations and other entities which provide services necessary to operations of the Company. This item would include, for instance, cash and securities advanced as [refundable] collateral for securities borrowed. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Audit and Accounting Guide (AAG) -Number AAG-BRD -Chapter 4 -Paragraph 80 -Subparagraph Exhibit 4-8, 4 -IssueDate 2006-05-01 -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 This item represents the gain realized during the period from the sale of trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27357-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 5 -Section 03 -Paragraph 7 -Subparagraph c Reference 3: 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)) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 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 + Details
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