9. Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Interest rate swaps [Member]
Derivative Instruments Maturity Period	2017-2027	2017-2026
Fair Value Notional Amount	$ 180.0	$ 101.1
Fair Value Assets	16.8	9.3
Fair Value Liabilities	8.2	3.5
Variance Swaps [member]
Derivative Instruments Maturity Period	2015-2017	2015-2017
Fair Value Notional Amount	0.9	0.9
Fair Value Assets		2.8
Fair Value Liabilities	3.1
Swaptions [Member]
Derivative Instruments Maturity Period	2024	2024
Fair Value Notional Amount	25.0	25.0
Fair Value Assets		0.2
Fair Value Liabilities
Put options [Member]
Derivative Instruments Maturity Period	2015-2022	2015-2022
Fair Value Notional Amount	391.0	200.0
Fair Value Assets	77.4	47.3
Fair Value Liabilities
Call options [Member]
Derivative Instruments Maturity Period	2012-2017	2012-2016
Fair Value Notional Amount	1,261.6	700.4
Fair Value Assets	74.0	28.0
Fair Value Liabilities	48.7	19.0
Equity futures
Derivative Instruments Maturity Period	2012	2012
Fair Value Notional Amount	182.1	66.3
Fair Value Assets	17.6	16.2
Fair Value Liabilities
Total derivative instruments
Fair Value Notional Amount	2,040.6	1,093.7
Fair Value Assets	185.8	103.8
Fair Value Liabilities	$ 60.0	$ 22.5