Derivative Financial Instruments (Details 2) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Derivatives, fair value disclosures
Total derivative instruments, assets	$ 706.6	$ 1,016.7
Total derivative instruments, liabilities	1,375.8	1,528.0
Fair value of embedded derivative liabilities reported with contractholder funds	74.2	170.5
Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	102.0	200.3
Total derivative instruments, liabilities	511.6	567.7
Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	604.6	816.4
Total derivative instruments, liabilities	864.2	960.3
Interest rate contracts | Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	0.2	10.3
Total derivative instruments, liabilities	350.5	440.5
Interest rate contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	506.4	677.1
Total derivative instruments, liabilities	449.0	493.9
Foreign exchange contracts | Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	101.8	190.0
Total derivative instruments, liabilities	161.1	127.2
Foreign exchange contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	43.5	58.2
Total derivative instruments, liabilities	23.7	14.3
Equity contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	45.1	74.3
Total derivative instruments, liabilities	77.2	27.7
Credit contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	9.6	6.8
Total derivative instruments, liabilities	63.4	96.6
Other contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, liabilities	$ 250.9	$ 327.8