Derivative Financial Instruments (Details 2) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Derivatives, fair value disclosures
Total derivative instruments, assets	$ 684.6	$ 1,016.7
Total derivative instruments, liabilities	1,262.3	1,528.0
Fair value of embedded derivative liabilities reported with contractholder funds	49.3	170.5
Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	121.8	200.3
Total derivative instruments, liabilities	391.0	567.7
Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	562.8	816.4
Total derivative instruments, liabilities	871.3	960.3
Interest rate contracts | Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	1.6	10.3
Total derivative instruments, liabilities	327.0	440.5
Interest rate contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	467.7	677.1
Total derivative instruments, liabilities	460.9	493.9
Foreign exchange contracts | Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	120.2	190.0
Total derivative instruments, liabilities	64.0	127.2
Foreign exchange contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	51.7	58.2
Total derivative instruments, liabilities	17.3	14.3
Equity contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	36.2	74.3
Total derivative instruments, liabilities	109.1	27.7
Credit contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	7.2	6.8
Total derivative instruments, liabilities	44.4	96.6
Other contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, liabilities	$ 239.6	$ 327.8