Derivative Financial Instruments (Details 2) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Derivatives, fair value disclosures
Total derivative instruments, assets	$ 1,136.3	$ 1,171.1
Total derivative instruments, liabilities	1,746.9	1,860.0
Fair value of embedded derivative liabilities reported with contractholder funds	179.4	195.8
Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	217.0	267.4
Total derivative instruments, liabilities	640.5	659.3
Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	919.3	903.7
Total derivative instruments, liabilities	1,106.4	1,200.7
Interest rate contracts | Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	12.0	0.2
Total derivative instruments, liabilities	486.3	500.9
Interest rate contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	757.5	730.9
Total derivative instruments, liabilities	605.4	651.5
Foreign exchange contracts | Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	205.0	267.2
Total derivative instruments, liabilities	154.2	158.4
Foreign exchange contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	41.3	38.5
Total derivative instruments, liabilities	38.8	42.7
Equity contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	112.0	120.3
Total derivative instruments, liabilities	3.4	0.8
Credit contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	8.5	14.0
Total derivative instruments, liabilities	141.4	169.7
Other contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, liabilities	$ 317.4	$ 336.0