Investments (Schedule Of Trading Securities) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Equity securities and other invested assets [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	$ 1,022.3	$ 1,243.2
Trading securities, Amortized Cost	972.3	1,166.2
Equity securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	202.3	403.0
Trading securities, Amortized Cost	205.3	395.3
Other invested assets [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	820.0	840.2
Trading securities, Amortized Cost	767.0	770.9
Fixed Maturities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	7,794.2	7,201.5
Trading securities, Amortized Cost	7,769.0	7,290.6
U.S. Government And Government Agencies [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	1,805.5	1,434.0
Trading securities, Amortized Cost	1,792.2	1,437.9
Non-U.S. Government And Government Agencies [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	469.6	556.8
Trading securities, Amortized Cost	479.8	579.2
States, Municipalities And Political Subdivisions [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	504.6	413.5
Trading securities, Amortized Cost	476.4	396.0
Corporate Debt, Financial Institutions [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	1,223.6	1,275.4
Trading securities, Amortized Cost	1,205.8	1,277.3
Corporate Debt, Industrials [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	1,476.8	1,308.1
Trading securities, Amortized Cost	1,461.5	1,345.6
Corporate Debt, Utilities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	140.4	118.9
Trading securities, Amortized Cost	140.3	125.4
Agency mortgage-backed [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	757.0	751.8
Trading securities, Amortized Cost	742.1	745.4
Non-agency residential mortgage-backed [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	24.0	34.0
Trading securities, Amortized Cost	23.1	32.4
Commercial mortgage-backed [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	604.2	582.8
Trading securities, Amortized Cost	637.0	600.1
Asset-backed [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	788.5	726.2
Trading securities, Amortized Cost	$ 810.8	$ 751.1