Derivative Instruments Derivative Instrument Gains (Losses) Recognized in Realized Investment Income (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Derivative [Line Items]
Total derivative instrument gains (losses) recognized in realized investment gains (losses)	$ (5.5)	$ (41.3)	$ (18.0)
Interest rate swaps
Derivative [Line Items]
Total derivative instrument gains (losses) recognized in realized investment gains (losses)	(11.4)	(1.7)	6.9
Variance swaps
Derivative [Line Items]
Total derivative instrument gains (losses) recognized in realized investment gains (losses)	(3.6)	(7.9)	3.5
Swaptions
Derivative [Line Items]
Total derivative instrument gains (losses) recognized in realized investment gains (losses)	17.3	(0.2)	(0.8)
Put options
Derivative [Line Items]
Total derivative instrument gains (losses) recognized in realized investment gains (losses)	(40.7)	(20.9)	10.6
Call options
Derivative [Line Items]
Total derivative instrument gains (losses) recognized in realized investment gains (losses)	60.1	0.9	(8.9)
Equity futures
Derivative [Line Items]
Total derivative instrument gains (losses) recognized in realized investment gains (losses)	(44.8)	(19.2)	(5.1)
Embedded derivatives
Derivative [Line Items]
Total derivative instrument gains (losses) recognized in realized investment gains (losses)	17.6	11.2	(33.2)
Related party reinsurance derivatives
Derivative [Line Items]
Total derivative instrument gains (losses) recognized in realized investment gains (losses)	$ 0	$ (3.5)	$ 9.0