Derivative Instruments - Gains (Losses) Recognized in Realized Investment Gains (Losses) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Derivative Instruments, Gain (Loss) [Line Items]
Total derivative instrument losses recognized in realized investment gains (losses)	$ (35.3)	$ (21.5)
Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Total derivative instrument losses recognized in realized investment gains (losses)	5.0	(0.8)
Variance swaps
Derivative Instruments, Gain (Loss) [Line Items]
Total derivative instrument losses recognized in realized investment gains (losses)	(0.6)	(2.1)
Swaptions
Derivative Instruments, Gain (Loss) [Line Items]
Total derivative instrument losses recognized in realized investment gains (losses)	(18.3)	(1.8)
Put options
Derivative Instruments, Gain (Loss) [Line Items]
Total derivative instrument losses recognized in realized investment gains (losses)	(4.0)	(16.8)
Call options
Derivative Instruments, Gain (Loss) [Line Items]
Total derivative instrument losses recognized in realized investment gains (losses)	(3.1)	17.0
Equity futures
Derivative Instruments, Gain (Loss) [Line Items]
Total derivative instrument losses recognized in realized investment gains (losses)	(2.6)	(16.4)
Embedded derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Total derivative instrument losses recognized in realized investment gains (losses)	$ (11.7)	$ (0.6)