Derivative Instruments - Gains (Losses) Recognized in Realized Investment Gains (Losses) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Total derivative instrument gains (losses) recognized in realized investment gains (losses)	$ (5.6)	$ (15.6)	$ (16.4)	$ (30.9)
Interest Rate Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total derivative instrument gains (losses) recognized in realized investment gains (losses)	(2.9)	(1.1)	(8.9)	(0.3)
Variance Swap [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total derivative instrument gains (losses) recognized in realized investment gains (losses)	(1.2)	(1.8)	(3.0)	(6.4)
Swaptions [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total derivative instrument gains (losses) recognized in realized investment gains (losses)	(4.7)	0	8.9	(0.2)
Put Option [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total derivative instrument gains (losses) recognized in realized investment gains (losses)	(8.5)	(11.8)	(29.1)	(13.7)
Call Option [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total derivative instrument gains (losses) recognized in realized investment gains (losses)	10.9	7.5	30.6	7.5
Equity futures [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total derivative instrument gains (losses) recognized in realized investment gains (losses)	(7.6)	(10.8)	(28.6)	(20.4)
Embedded Derivative Financial Instruments
Derivative Instruments, Gain (Loss) [Line Items]
Total derivative instrument gains (losses) recognized in realized investment gains (losses)	8.4	6.6	13.7	6.1
Related party reinsurance derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total derivative instrument gains (losses) recognized in realized investment gains (losses)	$ 0	$ (4.2)	$ 0	$ (3.5)