Derivative Financial Instruments (Details 2) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Derivatives, fair value disclosures
Total derivative instruments, assets	$ 608.0	$ 665.1
Total derivative instruments, liabilities	1,161.6	1,248.7
Fair value of embedded derivative liabilities reported with contractholder funds	25.8	6.9
Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	97.8	121.7
Total derivative instruments, liabilities	303.6	336.6
Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	510.2	543.4
Total derivative instruments, liabilities	858.0	912.1
Interest rate contracts | Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	0.3	0.1
Total derivative instruments, liabilities	256.4	285.4
Interest rate contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	434.5	452.2
Total derivative instruments, liabilities	387.6	489.6
Foreign exchange contracts | Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	97.5	121.6
Total derivative instruments, liabilities	47.2	51.2
Foreign exchange contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	48.3	51.6
Total derivative instruments, liabilities	25.1	17.9
Equity contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	17.7	30.0
Total derivative instruments, liabilities	160.5	145.0
Credit contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	9.7	9.6
Total derivative instruments, liabilities	30.1	35.5
Other contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, liabilities	$ 254.7	$ 224.1