Derivative Financial Instruments (Details 2) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Derivatives, fair value disclosures
Total derivative instruments, assets	$ 971.3	$ 1,171.1
Total derivative instruments, liabilities	1,668.3	1,860.0
Fair value of embedded derivative liabilities reported with contractholder funds	129.0	195.8
Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	206.6	267.4
Total derivative instruments, liabilities	608.5	659.3
Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	764.7	903.7
Total derivative instruments, liabilities	1,059.8	1,200.7
Interest rate contracts | Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets		0.2
Total derivative instruments, liabilities	476.8	500.9
Interest rate contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	624.0	730.9
Total derivative instruments, liabilities	593.6	651.5
Foreign exchange contracts | Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	206.6	267.2
Total derivative instruments, liabilities	131.7	158.4
Foreign exchange contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	55.1	38.5
Total derivative instruments, liabilities	34.5	42.7
Equity contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	78.3	120.3
Total derivative instruments, liabilities	27.2	0.8
Credit contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	7.3	14.0
Total derivative instruments, liabilities	140.6	169.7
Other contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, liabilities	$ 263.9	$ 336.0