Investments (Schedule Of Trading Securities) (Details) - USD ($) $ in Millions	Mar. 31, 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	$ 1,018.9	$ 1,243.2
Trading securities, Amortized Cost	972.1	1,166.2
Equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	202.0	403.0
Trading securities, Amortized Cost	209.4	395.3
Other invested assets
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	817.0	840.2
Trading securities, Amortized Cost	762.7	770.9
Fixed Maturities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	7,568.1	7,201.5
Trading securities, Amortized Cost	7,595.1	7,290.6
U.S. Government And Government Agencies [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	1,528.0	1,434.0
Trading securities, Amortized Cost	1,521.0	1,437.9
Non-U.S. government and government agencies
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	531.4	556.8
Trading securities, Amortized Cost	532.3	579.2
States, municipalities and political subdivisions
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	412.9	413.5
Trading securities, Amortized Cost	397.6	396.0
Corporate Debt: Financial institutions
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	1,369.7	1,275.4
Trading securities, Amortized Cost	1,354.2	1,277.3
Corporate debt: Industrials
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	1,435.6	1,308.1
Trading securities, Amortized Cost	1,440.7	1,345.6
Corporate debt: Utilities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	130.6	118.9
Trading securities, Amortized Cost	134.9	125.4
Agency mortgage-backed
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	786.0	751.8
Trading securities, Amortized Cost	773.0	745.4
Non-agency residential mortgage-backed
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	30.7	34.0
Trading securities, Amortized Cost	29.5	32.4
Commercial mortgage-backed
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	564.8	582.8
Trading securities, Amortized Cost	604.6	600.1
Asset-backed
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	778.4	726.2
Trading securities, Amortized Cost	$ 807.3	$ 751.1