Investment Securities (Fair Value Measurement by Level) (Details) (USD $) In Millions, unless otherwise specified																																																																																																																																																																																																																																																																																										12 Months Ended	9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014 Fair Value	Dec. 31, 2013 Fair Value	Sep. 30, 2013 Fair Value	Dec. 31, 2012 Fair Value	Sep. 30, 2014 Level 1 Inputs	Dec. 31, 2013 Level 1 Inputs	Sep. 30, 2013 Level 1 Inputs	Dec. 31, 2012 Level 1 Inputs	Sep. 30, 2014 Level 2 Inputs	Dec. 31, 2013 Level 2 Inputs	Sep. 30, 2013 Level 2 Inputs	Dec. 31, 2012 Level 2 Inputs	Sep. 30, 2014 Debt securities issued by corporations	Dec. 31, 2013 Debt securities issued by corporations	Sep. 30, 2014 Mortgage-backed and asset-backed securities Fair Value	Dec. 31, 2013 Mortgage-backed and asset-backed securities Fair Value	Sep. 30, 2014 Mortgage-backed and asset-backed securities Level 2 Inputs	Dec. 31, 2013 Mortgage-backed and asset-backed securities Level 2 Inputs	Sep. 30, 2014 Mortgage-backed and asset-backed securities Level 3 Inputs	Dec. 31, 2013 Mortgage-backed and asset-backed securities Level 3 Inputs	Sep. 30, 2014 Fixed maturity investments. Level 3 Inputs	Dec. 31, 2013 Fixed maturity investments. Level 3 Inputs	Sep. 30, 2013 Fixed maturity investments. Level 3 Inputs	Dec. 31, 2012 Fixed maturity investments. Level 3 Inputs	Sep. 30, 2014 Common equity securities Level 3 Inputs	Dec. 31, 2013 Common equity securities Level 3 Inputs	Sep. 30, 2013 Common equity securities Level 3 Inputs	Dec. 31, 2012 Common equity securities Level 3 Inputs	Sep. 30, 2014 Convertible fixed maturity investments Level 3 Inputs	Dec. 31, 2013 Convertible fixed maturity investments Level 3 Inputs	Sep. 30, 2013 Convertible fixed maturity investments Level 3 Inputs	Dec. 31, 2012 Convertible fixed maturity investments Level 3 Inputs	Sep. 30, 2014 Other long-term investments Level 3 Inputs	Dec. 31, 2013 Other long-term investments Level 3 Inputs	Sep. 30, 2013 Other long-term investments Level 3 Inputs	Dec. 31, 2012 Other long-term investments Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis U.S. Government and agency obligations Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis U.S. Government and agency obligations Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis U.S. Government and agency obligations Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis U.S. Government and agency obligations Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis U.S. Government and agency obligations Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis U.S. Government and agency obligations Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis U.S. Government and agency obligations Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis U.S. Government and agency obligations Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Financials Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Financials Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Financials Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Financials Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Financials Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Financials Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Financials Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Financials Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Communications [Member] Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Communications [Member] Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Communications [Member] Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Communications [Member] Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Communications [Member] Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Communications [Member] Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Communications [Member] Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Communications [Member] Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Energy Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Energy Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Energy Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Energy Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Energy Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Energy Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Energy Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Technology Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Technology Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Technology Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Technology Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Technology Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Technology Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Technology Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Technology Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Basic Materials [Member] Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Basic Materials [Member] Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Basic Materials [Member] Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Basic Materials [Member] Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Basic Materials [Member] Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Basic Materials [Member] Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Basic Materials [Member] Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Basic Materials [Member] Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Other: Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Other: Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Other: Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Other: Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Other: Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Other: Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Debt securities issued by corporations Other: Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Other: Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Municipal obligations Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Municipal obligations Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Municipal obligations Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Municipal obligations Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Municipal obligations Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Municipal obligations Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Municipal obligations Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Municipal obligations Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Preferred Stock Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Preferred Stock Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Preferred Stock Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Preferred Stock Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Preferred Stock Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Preferred Stock Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Preferred Stock Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Preferred Stock Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Fixed maturity investments. Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Fixed maturity investments. Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Fixed maturity investments. Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Fixed maturity investments. Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Fixed maturity investments. Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Fixed maturity investments. Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Fixed maturity investments. Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Fixed maturity investments. Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Short-term investments Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Short-term investments Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Short-term investments Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Short-term investments Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Short-term investments Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Short-term investments Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Short-term investments Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Short-term investments Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Short-term investments Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Short-term investments Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Consumer Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Consumer Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Consumer Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Consumer Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Consumer Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Consumer Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Consumer Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Consumer Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Industrial Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Industrial Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Industrial Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Industrial Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Industrial Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Industrial Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Industrial Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Industrial Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Financials Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Financials Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Financials Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Financials Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Financials Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Financials Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Financials Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Financials Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Communications [Member] Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Communications [Member] Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Communications [Member] Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Communications [Member] Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Communications [Member] Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Communications [Member] Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Communications [Member] Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Communications [Member] Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Energy Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Energy Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Energy Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Energy Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Energy Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Energy Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Energy Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Energy Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Technology Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Technology Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Technology Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Technology Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Technology Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Technology Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Technology Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Technology Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Utilities Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Utilities Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Utilities Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Utilities Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Utilities Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Utilities Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Utilities Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Utilities Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Basic Materials [Member] Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Basic Materials [Member] Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Basic Materials [Member] Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Basic Materials [Member] Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Basic Materials [Member] Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Basic Materials [Member] Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Basic Materials [Member] Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Basic Materials [Member] Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Other: Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Other: Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Other: Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Other: Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Other: Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Other: Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Other: Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Other: Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Common equity securities Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Common equity securities Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Convertible fixed maturity investments Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Convertible fixed maturity investments Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Convertible fixed maturity investments Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Convertible fixed maturity investments Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Convertible fixed maturity investments Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Convertible fixed maturity investments Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Convertible fixed maturity investments Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Convertible fixed maturity investments Level 3 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Other long-term investments Fair Value	Dec. 31, 2013 Fair value measured on a recurring basis Other long-term investments Fair Value	Sep. 30, 2014 Fair value measured on a recurring basis Other long-term investments Level 1 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Other long-term investments Level 1 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Other long-term investments Level 2 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Other long-term investments Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Other long-term investments Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Other long-term investments Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Other long-term investments Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Other long-term investments Level 3 Inputs	Dec. 31, 2013 Fair value measured on a recurring basis Forward Contracts Level 2 Inputs	Sep. 30, 2014 Fair value measured on a recurring basis Forward Contracts Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Forward Contracts Level 3 Inputs	Sep. 30, 2014 Segment, Discontinued Operations	Dec. 31, 2013 Segment, Discontinued Operations	Sep. 30, 2013 Segment, Discontinued Operations	Dec. 31, 2012 Segment, Discontinued Operations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments			$ 6,321.6	$ 6,766.5	$ 6,622.4	$ 6,950.7	$ 1,089.9	$ 1,376.7	$ 1,370.5	$ 1,355.1	$ 4,785.2	$ 4,982.2	$ 4,761.9	$ 5,206.1	$ 2,387.3	$ 2,347.2	$ 1,864.9	$ 2,014.5	$ 1,842.9	$ 1,992.5	$ 22.0	$ 22.0	$ 99.5	$ 93.0	$ 180.0	$ 92.9	$ 38.9	$ 46.1	$ 36.8	$ 37.3	$ 10.9	$ 6.1	$ 0	$ 0	$ 297.2	$ 262.4	$ 273.2	$ 259.3	$ 7,156.5	$ 7,402.4	$ 1,923.8	$ 1,998.2	$ 4,786.2	$ 4,996.6	$ 446.5	$ 407.6	$ 259.7	$ 362.5	$ 197.1	$ 295.8	$ 62.6	$ 66.7	$ 0	$ 0	$ 2,387.3	$ 2,347.2	$ 0	$ 0	$ 2,381.3	$ 2,347.2	$ 6.0	$ 0	$ 680.5	$ 754.4	$ 0	$ 0	$ 680.5	$ 754.4	$ 0	$ 0	$ 407.8	$ 281.1	$ 0	$ 0	$ 407.8	$ 281.1	$ 0	$ 0	$ 476.4	$ 434.4	$ 0	$ 0	$ 476.4	$ 434.4	$ 0	$ 0	$ 260.3	$ 265.0	$ 0	$ 0	$ 260.3	$ 265.0	$ 0	$ 0	$ 179.8	$ 159.7	$ 0	$ 0	$ 179.8	$ 159.7	$ 0	$ 56.8	$ 91.2	$ 0	$ 0	$ 56.8	$ 91.2	$ 0	$ 0	$ 161.1	$ 173.6	$ 0	$ 0	$ 161.1	$ 173.6	$ 0	$ 0	$ 140.7	$ 149.1	$ 0	$ 0	$ 134.7	$ 149.1	$ 6.0	$ 0	$ 23.9	$ 38.7	$ 0	$ 0	$ 23.9	$ 38.7	$ 0	$ 0	$ 79.9	$ 17.9	$ 0	$ 0	$ 79.9	$ 17.9	$ 0	$ 0	$ 1,864.9	$ 2,014.5	$ 0	$ 0	$ 1,842.9	$ 1,992.5	$ 22.0	$ 22.0	$ 311.2	$ 439.9	$ 22.1	$ 44.5	$ 289.1	$ 395.4	$ 0	$ 0	$ 86.4	$ 84.8	$ 0	$ 0	$ 14.9	$ 13.8	$ 71.5	$ 71.0	$ 4,989.4	$ 5,266.8	$ 219.2	$ 340.3	$ 4,670.7	$ 4,833.5	$ 99.5	$ 93.0	$ 834.9	$ 635.9	$ 833.9	$ 621.5			$ 1.0	$ 14.4	$ 0	$ 0	$ 277.5	$ 308.2	$ 277.2	$ 308.2	$ 0.3	$ 0	$ 0	$ 0	$ 97.1	$ 105.4	$ 97.1	$ 105.4	$ 0	$ 0	$ 0	$ 0	$ 296.4	$ 360.4	$ 257.5	$ 314.3	$ 0	$ 0	$ 38.9	$ 46.1	$ 54.6	$ 57.1	$ 54.6	$ 57.1	$ 0	$ 0	$ 0	$ 0	$ 58.8	$ 78.6	$ 58.8	$ 78.6	$ 0	$ 0	$ 0	$ 0	$ 36.8	$ 60.6	$ 36.8	$ 60.6	$ 0	$ 0	$ 0	$ 0	$ 22.3	$ 34.3	$ 22.3	$ 34.3	$ 0	$ 0	$ 0	$ 0	$ 38.9	$ 53.4	$ 38.9	$ 53.4	$ 0	$ 0	$ 0	$ 0	$ 103.7	$ 98.8	$ 27.5	$ 24.5	$ 76.2	$ 74.3	$ 0	$ 0	$ 986.1	$ 1,156.8	$ 870.7	$ 1,036.4	$ 76.5	$ 74.3	$ 38.9	$ 46.1	$ 48.9	$ 80.5	$ 0	$ 0	$ 38.0	$ 74.4	$ 10.9	$ 6.1	$ 297.2	$ 262.4	$ 0	$ 0	$ 0	$ 0	$ 297.2	$ 262.4
Carrying value of investment accounted for using the equity method																																																																																																																																																																																																																																																																																						23.5	26.6	26.9	35.0
Realized and unrealized gains (losses)																																																																																																																																																																																																																																																																																										(0.1)	0.2	(0.1)
Fixed maturity investments reclassified to assets held for sale		236.3																																																																																																																																																																																																																																																																																											203.9	236.3	239.7	338.1
Short-term investments, at amortized cost (which approximates fair value)	$ 834.9	$ 635.9																																																																																																																																																																														$ 834.9	$ 635.9	$ 648.0	$ 630.6