Derivative Financial Instruments (Details 2) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Derivatives, fair value disclosures
Total derivative instruments, assets	$ 840.9	$ 1,016.7
Total derivative instruments, liabilities	1,491.2	1,528.0
Fair value of embedded derivative liabilities reported with contractholder funds	117.8	170.5
Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	124.3	200.3
Total derivative instruments, liabilities	575.6	567.7
Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	716.6	816.4
Total derivative instruments, liabilities	915.6	960.3
Interest rate contracts | Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	5.9	10.3
Total derivative instruments, liabilities	404.7	440.5
Interest rate contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	605.2	677.1
Total derivative instruments, liabilities	468.6	493.9
Foreign exchange contracts | Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	118.4	190.0
Total derivative instruments, liabilities	170.9	127.2
Foreign exchange contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	52.6	58.2
Total derivative instruments, liabilities	15.0	14.3
Equity contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	50.8	74.3
Total derivative instruments, liabilities	67.8	27.7
Credit contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	8.0	6.8
Total derivative instruments, liabilities	71.1	96.6
Other contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, liabilities	$ 293.1	$ 327.8