Fair Value Measurements (Details 3) (Recurring Fair Value Measurements, USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Available-for-sale | Fixed maturities
Fair Value Hierarchy Levels Transfers
Transfers out of Level 2 into Level 3	$ 16.4	$ 19.7	$ 53.4	$ 154.2
Transfers out of Level 3 into Level 2	17.9	32.1	62.3	104.4
Available-for-sale | Corporate debt securities
Fair Value Hierarchy Levels Transfers
Transfers out of Level 2 into Level 3	15.7	4.7	46.6	105.3
Transfers out of Level 3 into Level 2		29.5	6.1	79.6
Available-for-sale | Collateralized debt obligations
Fair Value Hierarchy Levels Transfers
Transfers out of Level 2 into Level 3				31.7
Transfers out of Level 3 into Level 2	16.5	2.6	24.0	24.8
Available-for-sale | Other debt obligations
Fair Value Hierarchy Levels Transfers
Transfers out of Level 2 into Level 3		15.0		17.2
Transfers out of Level 3 into Level 2			29.7
Available-for-sale | Commercial mortgage-backed securities
Fair Value Hierarchy Levels Transfers
Transfers out of Level 2 into Level 3	0.7		6.8
Transfers out of Level 3 into Level 2	1.4		2.5
Available-for-sale | Equity securities
Fair Value Hierarchy Levels Transfers
Transfers out of Level 2 into Level 3			0.2
Separate account assets
Fair Value Hierarchy Levels Transfers
Transfers out of Level 1 into Level 2	2.1	7.1	17.5	250.9
Transfers out of Level 1 into Level 3				0.1
Transfers out of Level 2 into Level 1	17.5	6.9	71.3	11.7
Transfers out of Level 2 into Level 3	2.3	4.9	4.4	12.6
Transfers out of Level 3 into Level 2	$ 4.2	$ 6.3	$ 11.7	$ 6.5