Derivative Financial Instruments (Details 2) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Derivatives, fair value disclosures
Total derivative instruments, assets	$ 1,171.1	$ 1,083.2
Total derivative instruments, liabilities	1,860.0	1,416.9
Fair value of embedded derivative liabilities reported with contractholder funds	195.8	6.6
Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	267.4	457.4
Total derivative instruments, liabilities	659.3	547.9
Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	903.7	625.8
Total derivative instruments, liabilities	1,200.7	869.0
Interest rate contracts | Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	0.2	66.6
Total derivative instruments, liabilities	500.9	405.4
Interest rate contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	730.9	488.4
Total derivative instruments, liabilities	651.5	459.5
Foreign exchange contracts | Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	267.2	390.8
Total derivative instruments, liabilities	158.4	142.5
Foreign exchange contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	38.5	65.8
Total derivative instruments, liabilities	42.7	60.4
Equity contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	120.3	64.9
Total derivative instruments, liabilities	1.0	31.7
Credit contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	14.0	6.7
Total derivative instruments, liabilities	169.5	171.7
Other contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, liabilities	$ 336.0	$ 145.7