Derivative Financial Instruments (Details 2) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Derivatives, fair value disclosures
Total derivative instruments, assets	$ 1,127.4	$ 1,171.1
Total derivative instruments, liabilities	1,714.4	1,860.0
Fair value of embedded derivative liabilities reported with contractholder funds	221.7	195.8
Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	216.1	267.4
Total derivative instruments, liabilities	616.0	659.3
Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	911.3	903.7
Total derivative instruments, liabilities	1,098.4	1,200.7
Interest rate contracts | Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	14.1	0.2
Total derivative instruments, liabilities	478.8	500.9
Interest rate contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	758.1	730.9
Total derivative instruments, liabilities	571.8	651.5
Foreign exchange contracts | Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	202.0	267.2
Total derivative instruments, liabilities	137.2	158.4
Foreign exchange contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	61.3	38.5
Total derivative instruments, liabilities	33.5	42.7
Equity contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	85.6	120.3
Total derivative instruments, liabilities	14.7	0.8
Credit contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	6.3	14.0
Total derivative instruments, liabilities	114.2	169.7
Other contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, liabilities	$ 364.2	$ 336.0