Investment Securities (Fair Value Measurement by Level) (Details) (USD $)	3 Months Ended		9 Months Ended																																																																																																																																																																																																					9 Months Ended																																																																																																																		9 Months Ended	12 Months Ended				9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 Fair Value		Dec. 31, 2012 Fair Value		Sep. 30, 2012 Fair Value		Dec. 31, 2011 Fair Value		Sep. 30, 2013 Level 1 Inputs		Dec. 31, 2012 Level 1 Inputs		Sep. 30, 2012 Level 1 Inputs		Dec. 31, 2011 Level 1 Inputs		Sep. 30, 2013 Level 2 Inputs	Dec. 31, 2012 Level 2 Inputs	Sep. 30, 2012 Level 2 Inputs	Dec. 31, 2011 Level 2 Inputs	Sep. 30, 2013 Debt securities issued by corporations		Dec. 31, 2012 Debt securities issued by corporations		Sep. 30, 2013 Mortgage-backed and asset-backed securities Fair Value	Dec. 31, 2012 Mortgage-backed and asset-backed securities Fair Value	Sep. 30, 2013 Mortgage-backed and asset-backed securities Level 2 Inputs	Dec. 31, 2012 Mortgage-backed and asset-backed securities Level 2 Inputs	Sep. 30, 2013 Mortgage-backed and asset-backed securities Level 3 Inputs	Dec. 31, 2012 Mortgage-backed and asset-backed securities Level 3 Inputs	Sep. 30, 2013 Fixed maturity investments. Level 3 Inputs	Dec. 31, 2012 Fixed maturity investments. Level 3 Inputs	Sep. 30, 2012 Fixed maturity investments. Level 3 Inputs	Dec. 31, 2011 Fixed maturity investments. Level 3 Inputs	Sep. 30, 2013 Common equity securities Level 3 Inputs	Dec. 31, 2012 Common equity securities Level 3 Inputs	Sep. 30, 2012 Common equity securities Level 3 Inputs	Dec. 31, 2011 Common equity securities 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, 2012 Convertible fixed maturity investments Level 3 Inputs	Dec. 31, 2011 Convertible fixed maturity 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, 2012 Other long-term investments Level 3 Inputs		Dec. 31, 2011 Other long-term investments Level 3 Inputs		Sep. 30, 2013 Fair value measured on a recurring basis Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis U.S. Government and agency obligations Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis U.S. Government and agency obligations Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis U.S. Government and agency obligations Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis U.S. Government and agency obligations Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis U.S. Government and agency obligations Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis U.S. Government and agency obligations Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis U.S. Government and agency obligations Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis U.S. Government and agency obligations Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Consumer Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Industrial Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Financials Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Financials Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Financials Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Financials Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Financials Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Financials Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Financials Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Financials Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Communications Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Communications Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Communications Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Communications Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Communications Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Communications Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Communications Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Communications Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Basic materials Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Basic materials Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Basic materials Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Basic materials Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Basic materials Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Basic materials Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Basic materials Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Basic materials Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Energy Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Energy Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Energy Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Energy Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Energy Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Energy Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Energy Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Energy Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Utilities Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Technology Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Technology Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Technology Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Technology Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Technology Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Technology Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Technology Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Technology Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Other: Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Other: Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Other: Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Other: Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Other: Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Other: Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Debt securities issued by corporations Other: Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Debt securities issued by corporations Other: Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Municipal obligations Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Municipal obligations Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Municipal obligations Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Municipal obligations Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Municipal obligations Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Municipal obligations Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Municipal obligations Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Municipal obligations Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Mortgage-backed and asset-backed securities Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Foreign government, agency and provincial obligations Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Preferred Stock Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Preferred Stock Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Preferred Stock Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Preferred Stock Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Preferred Stock Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Preferred Stock Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Preferred Stock Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Preferred Stock Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Fixed maturity investments. Fair Value		Dec. 31, 2012 Fair value measured on a recurring basis Fixed maturity investments. Fair Value		Sep. 30, 2013 Fair value measured on a recurring basis Fixed maturity investments. Level 1 Inputs		Dec. 31, 2012 Fair value measured on a recurring basis Fixed maturity investments. Level 1 Inputs		Sep. 30, 2013 Fair value measured on a recurring basis Fixed maturity investments. Level 2 Inputs		Dec. 31, 2012 Fair value measured on a recurring basis Fixed maturity investments. Level 2 Inputs		Sep. 30, 2013 Fair value measured on a recurring basis Fixed maturity investments. Level 3 Inputs		Dec. 31, 2012 Fair value measured on a recurring basis Fixed maturity investments. Level 3 Inputs		Sep. 30, 2013 Fair value measured on a recurring basis Short-term investments Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Short-term investments Fair Value	Sep. 30, 2013 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 1 Inputs	Dec. 31, 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, 2013 Fair value measured on a recurring basis Short-term investments Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Short-term investments Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Short-term investments Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Short-term investments Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Consumer Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Consumer Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Consumer Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Consumer Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Consumer Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Consumer Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Consumer Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Consumer Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Industrial Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Industrial Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Industrial Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Industrial Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Industrial Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Industrial Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Industrial Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Industrial Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Financials Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Financials Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Financials Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Financials Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Financials Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Financials Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Financials Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Financials Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Communications Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Communications Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Communications Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Communications Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Communications Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Communications Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Communications Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Communications Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Basic materials Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Basic materials Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Basic materials Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Basic materials Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Basic materials Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Basic materials Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Basic materials Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Basic materials Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Energy Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Energy Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Energy Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Energy Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Energy Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Energy Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Energy Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Energy Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Utilities Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Utilities Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Utilities Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Utilities Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Utilities Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Utilities Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Utilities Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Utilities Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Technology Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Technology Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Technology Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Technology Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Technology Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Technology Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Technology Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Technology Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Other: Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Other: Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Other: Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Other: Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Other: Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Other: Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Other: Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Other: Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Common equity securities Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Common equity securities Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Convertible fixed maturity investments Fair Value	Dec. 31, 2012 Fair value measured on a recurring basis Convertible fixed maturity investments Fair Value	Sep. 30, 2013 Fair value measured on a recurring basis Convertible fixed maturity investments Level 1 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Convertible fixed maturity investments Level 1 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Convertible fixed maturity investments Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Convertible fixed maturity investments Level 2 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Convertible fixed maturity investments Level 3 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Convertible fixed maturity investments Level 3 Inputs	Sep. 30, 2013 Fair value measured on a recurring basis Other long-term investments Fair Value		Dec. 31, 2012 Fair value measured on a recurring basis Other long-term investments Fair Value		Sep. 30, 2013 Fair value measured on a recurring basis Other long-term investments Level 1 Inputs		Dec. 31, 2012 Fair value measured on a recurring basis Other long-term investments Level 1 Inputs		Sep. 30, 2013 Fair value measured on a recurring basis Other long-term investments Level 2 Inputs		Dec. 31, 2012 Fair value measured on a recurring basis Other long-term investments Level 2 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		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, 2013 Fair value measured on a recurring basis Forward Contracts Level 2 Inputs	Dec. 31, 2012 Fair value measured on a recurring basis Forward Contracts Level 2 Inputs	Sep. 30, 2013 Segment, Discontinued Operations	Dec. 31, 2012 Segment, Discontinued Operations	Sep. 30, 2012 Segment, Discontinued Operations	Sep. 30, 2013 Prospector Offshore Fund Ltd [Member] Fair value measured on a recurring basis Short-term investments
Investment securities
Fair value investments	$ 1.3		$ 1.3			$ 6,622,400,000	[1],[2]	$ 6,950,700,000	[1],[2]	$ 6,709,100,000	[3],[4]	$ 7,500,800,000	[3],[4]	$ 1,370,500,000	[5]	$ 1,355,100,000	[5]	$ 1,308,500,000	[6]	$ 1,033,100,000	[6]	$ 4,761,900,000	$ 5,206,100,000	$ 5,016,000,000	$ 6,088,200,000	$ 2,317,200,000	[7]	$ 2,385,100,000	[7]	$ 1,915,800,000	$ 2,095,600,000	$ 1,806,500,000	$ 2,073,500,000	$ 109,300,000	$ 22,100,000	$ 180,000,000	$ 92,900,000	$ 76,100,000	$ 78,900,000	$ 36,800,000	$ 37,300,000	$ 35,900,000	$ 32,300,000	$ 0	$ 0	$ 0	$ 0	$ 273,200,000	$ 259,300,000	$ 272,600,000	[4]	$ 268,300,000	[3],[4]	$ 7,270,400,000	$ 7,581,300,000	$ 1,999,100,000	$ 1,985,700,000	$ 4,781,300,000	$ 5,206,100,000	$ 490,000,000	$ 389,500,000	$ 388,200,000	$ 440,100,000	$ 321,300,000	$ 369,100,000	$ 66,900,000	$ 71,000,000	$ 0	$ 0	$ 2,317,200,000	$ 2,385,100,000	$ 0	$ 1,000,000	$ 2,317,200,000	$ 2,384,100,000	$ 0	$ 0	$ 690,200,000	$ 727,100,000	$ 0	$ 0	$ 690,200,000	$ 727,100,000	$ 0	$ 0	$ 284,200,000	$ 330,800,000	$ 0	$ 0	$ 284,200,000	$ 330,800,000	$ 0	$ 0	$ 427,000,000	$ 401,400,000	$ 0	$ 1,000,000	$ 427,000,000	$ 400,400,000	$ 0	$ 0	$ 273,800,000	$ 276,100,000	$ 0	$ 0	$ 273,800,000	$ 276,100,000	$ 0	$ 0	$ 200,700,000	$ 189,100,000	$ 0	$ 0	$ 200,700,000	$ 189,100,000	$ 0	$ 0	$ 162,600,000	$ 181,500,000	$ 0	$ 0	$ 162,600,000	$ 181,500,000	$ 0	$ 0	$ 178,500,000	$ 204,200,000	$ 0	$ 0	$ 178,500,000	$ 204,200,000	$ 0	$ 0	$ 94,200,000	$ 54,000,000	$ 0	$ 0	$ 94,200,000	$ 54,000,000	$ 0	$ 0	$ 6,000,000	$ 20,900,000	$ 0	$ 0	$ 6,000,000	$ 20,900,000	$ 0	$ 0	$ 5,500,000	$ 5,200,000	$ 0	$ 0	$ 5,500,000	$ 5,200,000	$ 0	$ 0	$ 1,915,800,000	$ 2,095,600,000	$ 0	$ 0	$ 1,806,500,000	$ 2,073,500,000	$ 109,300,000	$ 22,100,000	$ 442,800,000	$ 521,900,000	$ 46,000,000	$ 52,100,000	$ 396,800,000	$ 469,800,000	$ 0	$ 0	$ 84,200,000	$ 86,400,000	$ 0	$ 0	$ 13,500,000	$ 15,600,000	$ 70,700,000	$ 70,800,000	$ 5,153,700,000	[1]	$ 5,534,300,000	[8]	$ 367,300,000	[1]	$ 422,200,000	[8]	$ 4,606,400,000	[1]	$ 5,019,200,000	[8]	$ 180,000,000	[1]	$ 92,900,000	[8]	$ 648,000,000	$ 630,600,000	$ 628,600,000		$ 630,600,000		$ 19,400,000	$ 0	$ 0	$ 0	$ 290,900,000	$ 255,600,000	$ 290,900,000	$ 255,600,000	$ 0	$ 0	$ 0	$ 0	$ 90,500,000	$ 41,900,000	$ 90,500,000	$ 41,900,000	$ 0	$ 0	$ 0	$ 0	$ 326,400,000	$ 324,500,000	$ 289,600,000	$ 286,300,000	$ 0	$ 900,000	$ 36,800,000	$ 37,300,000	$ 63,700,000	$ 35,200,000	$ 63,700,000	$ 35,200,000	$ 0	$ 0	$ 0	$ 0	$ 63,700,000	$ 103,300,000	$ 63,700,000	$ 103,300,000	$ 0	$ 0	$ 0	$ 0	$ 82,600,000	$ 101,000,000	$ 82,600,000	$ 101,000,000	$ 0	$ 0	$ 0	$ 0	$ 35,500,000	$ 43,600,000	$ 35,500,000	$ 43,400,000	$ 0	$ 200,000	$ 0	$ 0	$ 60,800,000	$ 55,000,000	$ 60,800,000	$ 55,000,000	$ 0	$ 0	$ 0	$ 0	$ 96,600,000	$ 69,600,000	$ 25,900,000	$ 11,200,000	$ 70,700,000	$ 58,400,000	$ 0	$ 0	$ 1,110,700,000	$ 1,029,700,000	$ 1,003,200,000	$ 932,900,000	$ 70,700,000	$ 59,500,000	$ 36,800,000	$ 37,300,000	$ 84,800,000	$ 127,400,000	$ 0	$ 0	$ 84,800,000	$ 127,400,000	$ 0	$ 0	$ 273,200,000	[2]	$ 259,300,000	[9]	$ 0	[2]	$ 0	[9]	$ 0	[2]	$ 0	[9]	$ 273,200,000	[2]	$ 259,300,000	[9]
Carrying value of investment accounted for using the equity method																																																																																																																																																																																																								648,000,000	917,300,000	630,600,000	846,000,000																																																																																																									26,900,000		35,000,000		33,000,000	34,000,000
Realized and unrealized (losses) gains																																																																																																																																																																																																																																																																																																																										(100,000)	(100,000)
Fixed maturity investments reclassified to assets held for sale					338,100,000																																																																																																																																																																																																																																																																																																																							(239,700,000)	338,100,000	111,800,000
Realized and unrealized gain	27,000,000	60,400,000	63,600,000	94,900,000																																																																																																																																																																																																				0.2	3,900,000
Net Realized and Unrealized Gain (Loss) on Trading Securities	28,200,000	72,700,000	66,100,000	123,200,000																																																																																																																																																																																																																																																																																																																											14.1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3			$ 90.3

[1] Carrying value includes $239.7 that is classified as assets held for sale relating to discontinued operations.

[2] Excludes carrying value of $26.9 associated with other long-term investment limited partnerships accounted for using the equity method and $(0.1) related to forward contracts

[3] Carrying value includes $111.8 that is classified as assets held for sale relating to discontinued operations.

[4] Excludes carrying value of $33.0 and $34.0 at January 1, 2012 and September 30, 2012 associated with other long-term investment limited partnerships accounted for using the equity method.

[5] Excludes carrying value of $630.6 and $648.0 at January 1, 2013 and September 30, 2013 and realized and unrealized gains for the periods of $0.2 associated with short-term investments

[6] Excludes carrying value of $846.0 and $917.3 at January 1, 2012 and September 30, 2012 and realized and unrealized loss for the period of $3.9 associated with short-term investment

[7] Credit ratings are assigned based on the following hierarchy: 1) Standard and Poor's Financial Services LLC ("Standard & Poor’s") and 2) Moody’s Investor Service ("Moody's").

[8] Carrying value includes $338.1 that is classified as assets held for sale relating to discontinued operations.

[9] Excludes carrying value of $35.0 associated with other long-term investment limited partnerships accounted for using the equity method and $(0.1) related to currency forward contracts.