Fair Value Measurements (Details 3) (Recurring Fair Value Measurements, USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Available-for-sale | Fixed maturities
Fair Value Hierarchy Levels Transfers
Transfers out of Level 2 into Level 3	$ 6.6	$ 68.9
Transfers out of Level 3 into Level 2	37.2	23.6
Available-for-sale | Corporate debt securities
Fair Value Hierarchy Levels Transfers
Transfers out of Level 2 into Level 3	0.5	47.5
Transfers out of Level 3 into Level 2		23.6
Available-for-sale | Commercial mortgage-backed securities
Fair Value Hierarchy Levels Transfers
Transfers out of Level 2 into Level 3	6.1
Available-for-sale | Collateralized debt obligations
Fair Value Hierarchy Levels Transfers
Transfers out of Level 2 into Level 3		21.4
Transfers out of Level 3 into Level 2	7.5
Available-for-sale | Other debt obligations
Fair Value Hierarchy Levels Transfers
Transfers out of Level 3 into Level 2	29.7
Separate account assets
Fair Value Hierarchy Levels Transfers
Transfers out of Level 1 into Level 2	3.7	243.4
Transfers out of Level 2 into Level 1	53.2	4.6
Transfers out of Level 2 into Level 3	2.0	1.4
Transfers out of Level 3 into Level 2	$ 5.8