Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Derivative [Line Items]
Fair Value Assets	$ 237.8		$ 149.4
Fair Value Liabilities	110.8		45.7
Interest rate swaps
Derivative [Line Items]
Notional Amount	139.0		180.0
Fair Value Assets	3.9		15.5
Fair Value Liabilities	6.8	[1]	7.7	[1]
Variance swaps
Derivative [Line Items]
Notional Amount	0.9		0.9
Fair Value Assets	0		0
Fair Value Liabilities	7.9	[1]	4.4	[1]
Swaptions
Derivative [Line Items]
Notional Amount	3,902.0		25.0
Fair Value Assets	30.7		0
Fair Value Liabilities	0	[1]	0	[1]
Put options
Derivative [Line Items]
Notional Amount	391.0		391.0
Fair Value Assets	29.5		69.5
Fair Value Liabilities	0	[1]	0	[1]
Call options
Derivative [Line Items]
Notional Amount	1,701.6		1,328.4
Fair Value Assets	161.2		50.6
Fair Value Liabilities	96.1	[1]	33.6	[1]
Equity futures
Derivative [Line Items]
Notional Amount	159.7		182.9
Fair Value Assets	12.5		13.8
Fair Value Liabilities	0	[1]	0	[1]
Total derivative instruments
Derivative [Line Items]
Notional Amount	6,294.2		2,108.2
Fair Value Assets	237.8		149.4
Fair Value Liabilities	$ 110.8	[1]	$ 45.7	[1]

[1] Derivative liabilities are included in other liabilities on the balance sheets.