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Investment Securities (Fair Value Measurement by Level) (Details) (USD $) In Millions, unless otherwise specified |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9 Months Ended |  |
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Sep. 30, 2012 Fair Value | Dec. 31, 2011 Fair Value | Sep. 30, 2011 Fair Value | Dec. 31, 2010 Fair Value | Sep. 30, 2012 Level 1 Inputs | Dec. 31, 2011 Level 1 Inputs | Sep. 30, 2011 Level 1 Inputs | Dec. 31, 2010 Level 1 Inputs | Sep. 30, 2012 Level 2 Inputs | Dec. 31, 2011 Level 2 Inputs | Sep. 30, 2011 Level 2 Inputs | Dec. 31, 2010 Level 2 Inputs | Dec. 31, 2010 Level 3 Inputs | Sep. 30, 2012 Debt securities issued by corporations | Dec. 31, 2011 Debt securities issued by corporations | Sep. 30, 2012 Mortgage-backed and asset-backed securities Fair Value | Dec. 31, 2011 Mortgage-backed and asset-backed securities Fair Value | Sep. 30, 2012 Mortgage-backed and asset-backed securities Level 2 Inputs | Dec. 31, 2011 Mortgage-backed and asset-backed securities Level 2 Inputs | Sep. 30, 2012 Mortgage-backed and asset-backed securities Level 3 Inputs | Dec. 31, 2011 Mortgage-backed and asset-backed securities Level 3 Inputs | Sep. 30, 2012 Fixed maturity investments. Level 3 Inputs | Dec. 31, 2011 Fixed maturity investments. Level 3 Inputs | Sep. 30, 2011 Fixed maturity investments. Level 3 Inputs | Dec. 31, 2010 Fixed maturity investments. Level 3 Inputs | Sep. 30, 2012 Common equity securities Level 3 Inputs | Dec. 31, 2011 Common equity securities Level 3 Inputs | Sep. 30, 2011 Common equity securities Level 3 Inputs | Dec. 31, 2010 Common equity securities Level 3 Inputs | Sep. 30, 2012 Convertible fixed maturity investments Level 3 Inputs | Dec. 31, 2011 Convertible fixed maturity investments Level 3 Inputs | Sep. 30, 2011 Convertible fixed maturity investments Level 3 Inputs | Sep. 30, 2012 Other long-term investments Level 3 Inputs | Dec. 31, 2011 Other long-term investments Level 3 Inputs | Sep. 30, 2011 Other long-term investments Level 3 Inputs | Dec. 31, 2010 Other long-term investments Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis U.S. Government and agency obligations Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis U.S. Government and agency obligations Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis U.S. Government and agency obligations Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis U.S. Government and agency obligations Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis U.S. Government and agency obligations Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis U.S. Government and agency obligations Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis U.S. Government and agency obligations Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis U.S. Government and agency obligations Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Financials Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Financials Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Financials Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Financials Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Financials Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Financials Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Financials Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Financials Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Communications Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Communications Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Communications Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Communications Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Communications Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Communications Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Communications Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Communications Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Basic materials Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Basic materials Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Basic materials Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Basic materials Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Basic materials Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Basic materials Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Basic materials Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Basic materials Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Energy Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Energy Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Energy Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Energy Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Energy Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Energy Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Energy Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Energy Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Technology Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Technology Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Technology Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Technology Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Technology Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Technology Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Technology Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Technology Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Diversified Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Diversified Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Diversified Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Diversified Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Diversified Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Diversified Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Diversified Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Debt securities issued by corporations Diversified Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Municipal obligations Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Municipal obligations Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Municipal obligations Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Municipal obligations Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Municipal obligations Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Municipal obligations Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Municipal obligations Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Municipal obligations Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Non-cumulative perpetual preference shares Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Non-cumulative perpetual preference shares Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Non-cumulative perpetual preference shares Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Non-cumulative perpetual preference shares Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Non-cumulative perpetual preference shares Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Non-cumulative perpetual preference shares Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Non-cumulative perpetual preference shares Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Non-cumulative perpetual preference shares Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Fixed maturity investments. Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Fixed maturity investments. Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Fixed maturity investments. Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Fixed maturity investments. Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Fixed maturity investments. Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Fixed maturity investments. Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Fixed maturity investments. Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Fixed maturity investments. Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Short-term investments Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Short-term investments Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Short-term investments Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Short-term investments Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Short-term investments Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Short-term investments Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Short-term investments Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Short-term investments Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Consumer Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Consumer Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Consumer Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Consumer Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Consumer Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Consumer Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Consumer Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Consumer Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Financials Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Financials Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Financials Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Financials Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Financials Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Financials Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Financials Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Financials Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Basic materials Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Basic materials Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Basic materials Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Basic materials Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Basic materials Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Basic materials Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Basic materials Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Basic materials Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Energy Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Energy Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Energy Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Energy Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Energy Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Energy Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Energy Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Energy Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Utilities Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Utilities Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Utilities Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Utilities Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Utilities Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Utilities Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Utilities Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Utilities Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Technology Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Technology Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Technology Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Technology Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Technology Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Technology Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Technology Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Technology Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Other: Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Other: Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Other: Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Other: Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Other: Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Other: Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Other: Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Other: Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Common equity securities Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Common equity securities Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Convertible fixed maturity investments Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Convertible fixed maturity investments Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Convertible fixed maturity investments Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Convertible fixed maturity investments Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Convertible fixed maturity investments Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Convertible fixed maturity investments Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Convertible fixed maturity investments Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Convertible fixed maturity investments Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Other long-term investments Fair Value | Dec. 31, 2011 Fair value measured on a recurring basis Other long-term investments Fair Value | Sep. 30, 2012 Fair value measured on a recurring basis Other long-term investments Level 1 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Other long-term investments Level 1 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Other long-term investments Level 2 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Other long-term investments Level 2 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Other long-term investments Level 3 Inputs | Dec. 31, 2011 Fair value measured on a recurring basis Other long-term investments Level 3 Inputs | Sep. 30, 2011 Fair value measured on a recurring basis Other long-term investments Level 3 Inputs | Dec. 31, 2010 Fair value measured on a recurring basis Other long-term investments Level 3 Inputs | Sep. 30, 2012 Fair value measured on a recurring basis Forward Contracts [Member] Level 2 Inputs | Sep. 30, 2012 Segment, Discontinued Operations [Member] | Dec. 31, 2011 Segment, Discontinued Operations [Member]
Investment securities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Fair value investments | $ 7,626.4 | [1] | $ 8,346.8 | [1],[2] | $ 7,265.9 | [1] | $ 7,901.6 | [1] | $ 2,225.8 | $ 1,879.1 | $ 1,755.2 | $ 1,894.4 | $ 5,016.0 | $ 6,088.2 | $ 4,969.5 | $ 5,477.4 | $ 0 | $ 2,281.3 | $ 2,135.1 | $ 2,047.4 | $ 3,222.9 | $ 2,041.9 | $ 3,207.8 | $ 5.5 | $ 15.1 | $ 76.1 | $ 78.9 | $ 216.9 | $ 128.4 | $ 35.9 | $ 32.3 | $ 32.1 | $ 71.2 | $ 0 | $ 0 | $ 0 | $ 272.6 | [1] | $ 268.3 | [1] | $ 292.2 | [1] | $ 330.2 | [1] | $ 7,626.4 | $ 8,346.8 | $ 2,225.8 | $ 1,879.1 | $ 5,016.0 | $ 6,088.2 | $ 384.6 | $ 379.5 | $ 394.7 | $ 305.0 | $ 340.5 | $ 296.2 | $ 54.2 | $ 8.8 | $ 0 | $ 0 | $ 2,281.3 | $ 2,135.1 | $ 1.1 | $ 3.8 | $ 2,280.2 | $ 2,131.3 | $ 0 | $ 0 | $ 597.2 | $ 790.7 | $ 0 | $ 0 | $ 597.2 | $ 790.7 | $ 0 | $ 0 | $ 488.1 | $ 359.4 | $ 0 | $ 0 | $ 488.1 | $ 359.4 | $ 0 | $ 0 | $ 405.4 | $ 239.6 | $ 1.1 | $ 3.8 | $ 404.3 | $ 235.8 | $ 0 | $ 0 | $ 217.1 | $ 225.8 | $ 0 | $ 0 | $ 217.1 | $ 225.8 | $ 0 | $ 0 | $ 175.1 | $ 195.7 | $ 0 | $ 0 | $ 175.1 | $ 195.7 | $ 0 | $ 0 | $ 172.9 | $ 155.8 | $ 0 | $ 0 | $ 172.9 | $ 155.8 | $ 0 | $ 0 | $ 204.4 | $ 140.1 | $ 0 | $ 0 | $ 204.4 | $ 140.1 | $ 0 | $ 0 | $ 21.1 | $ 24.5 | $ 0 | $ 0 | $ 21.1 | $ 24.5 | $ 0 | $ 0 | $ 0 | $ 3.5 | $ 0 | $ 0 | $ 0 | $ 3.5 | $ 0 | $ 0 | $ 3.8 | $ 2.7 | $ 0 | $ 0 | $ 3.8 | $ 2.7 | $ 0 | $ 0 | $ 2,047.4 | $ 3,222.9 | $ 0 | $ 0 | $ 2,041.9 | $ 3,207.8 | $ 5.5 | $ 15.1 | $ 476.4 | $ 589.2 | $ 56.9 | $ 65.7 | $ 419.5 | $ 523.5 | $ 0 | $ 0 | $ 86.1 | $ 78.8 | $ 0 | $ 0 | $ 15.5 | $ 15.0 | $ 70.6 | $ 63.8 | $ 5,289.7 | $ 6,333.7 | [3] | $ 398.5 | $ 365.7 | [3] | $ 4,815.1 | $ 5,889.1 | [3] | $ 76.1 | $ 78.9 | [3] | $ 917.3 | $ 846.0 | $ 917.3 | $ 846.0 | $ 0 | $ 0 | $ 0 | $ 0 | $ 249.7 | $ 188.8 | $ 249.6 | $ 188.5 | $ 0.1 | $ 0.3 | $ 0 | $ 0 | $ 316.1 | $ 219.2 | $ 277.9 | $ 185.8 | $ 2.3 | $ 1.5 | $ 35.9 | $ 31.9 | $ 118.2 | $ 121.0 | $ 118.2 | $ 119.9 | $ 0 | $ 1.1 | $ 0 | $ 0 | $ 96.8 | $ 72.6 | $ 96.8 | $ 72.6 | $ 0 | $ 0 | $ 0 | $ 0 | $ 42.9 | $ 42.0 | $ 42.7 | $ 41.8 | $ 0.2 | $ 0.2 | $ 0 | $ 0 | $ 51.6 | $ 25.8 | $ 51.6 | $ 25.8 | $ 0 | $ 0 | $ 0 | $ 0 | $ 129.5 | $ 85.6 | $ 73.2 | $ 33.0 | $ 56.3 | $ 52.2 | $ 0 | $ 0.4 | $ 1,004.8 | $ 755.0 | $ 910.0 | $ 667.4 | $ 58.9 | $ 55.3 | $ 35.9 | $ 32.3 | $ 142.0 | $ 143.8 | $ 0 | $ 0 | $ 142.0 | $ 143.8 | $ 0 | $ 0 | $ 272.6 | [3] | $ 268.3 | [4] | $ 0 | [3] | $ 0 | [4] | $ 0 | [3] | $ 0 | [4] | $ 272.6 | [3] | $ 268.3 | [4] |  |  |  |  |
Carrying value of investment accounted for using the equity method |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 34.3 |  | 33.0 |  | 36.6 | 41.9 |  |  |
Derivative, Gain (Loss) on Derivative, Net |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.3 |  |
Fixed maturity investments reclassified to assets held for sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 377.3 | $ 111.8
[1] | (1) Excludes carrying value of $33.0 and $34.3 at January 1, 2012 and September 30, 2012 associated with other long-term investments accounted for using the equity method
[2] | (2) Carrying value includes $111.8 and $377.3 at January 1, 2012 and September 30, 2012 that is classified as assets held for sale relating to discontinued operations. Level 3 Investments MillionsLevel 1InvestmentsLevel 2InvestmentsFixedMaturitiesCommonequitysecuritiesConvertiblefixedmaturitiesOther long-terminvestments Total Balance at January 1, 2011$1,894.4$5,477.4$128.4$71.2$—$330.2(1) $7,901.6(1) Total realized and unrealized gains (losses)(50.5)115.9(10.6)(4.9)—22.5 72.4 Foreign currency gains (losses) through OCI.3(84.4)(4.4)1.6—(5.0) (91.9) Amortization/Accretion2.4(40.7)(.1)——— (38.4) Purchases6,690.73,987.4212.819.7—27.9 10,938.5 Sales(6,782.1)(4,596.9)1.6(55.5)—(83.4) (11,516.3) Transfers in—111.81.0——— 112.8 Transfers out—(1.0)(111.8)——— (112.8) Balance at September 30, 2011$1,755.2$4,969.5$216.9$32.1$—$292.2(1) $7,265.9(1) (1) Excludes carrying value o
[3] | September 30, 2012MillionsFair value Level 1 Inputs Level 2 Inputs Level 3 InputsFixed maturity investments: US Government and agency obligations$394.7 $340.5 $54.2 $— Debt securities issued by corporations: Consumer597.2 — 597.2 —Industrial488.1 — 488.1 —Financials405.4 1.1 404.3 —Communications217.1 — 217.1 —Basic materials175.1 — 175.1 —Energy172.9 — 172.9 —Utilities204.4 — 204.4 —Technology21.1 — 21.1 —Diversified— — — —Total debt securities issued by corporations:2,281.3 1.1 2,280.2 — Municipal obligations3.8 — 3.8 —Mortgage-backed and asset-backed securities2,047.4 — 2,041.9 5.5Foreign government, agency and provincial obligations476.4 56.9 419.5 —Preferred stocks86.1 — 15.5 70.6Total fixed maturity investments (1)5,289.7 398.5 4,815.1 76.1 Short-term investments917.3 917.3 — — Common equity securities: Financials316.1 277.9 2.3 35.9Consumer249.7 249.6 .1 —Basic materials118.2 118.2 — —Energy96.8 96.8 — —Technology51.6 51.6 — —Utilities42.9 42.7 .2 —Other129.5 73.2 56.3 —Total common equity securities1,004.8 910.0 58.9 35.9 Convertible fixed maturity investments142.0 — 142.0 —Other long-term investments (2) 272.6 — — 272.6Total investments$7,626.4 $2,225.8 $5,016.0 $384.6 (1) Carrying value includes $377.3 that is classified as assets held for sale relating to discontinued operations. (2) Excludes carrying value of $34.3 associated with other long-term investment limited partnerships accounted for using the equity method and $0.3 related to forward contrac
[4] |

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