Derivative Financial Instruments (Details 2) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Derivatives, fair value disclosures
Total derivative instruments, assets	$ 589.6	$ 661.8
Total derivative instruments, liabilities	1,144.6	1,207.3
Fair value of embedded derivative liabilities reported with contractholder funds	117.0	176.4
Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	106.2	88.8
Total derivative instruments, liabilities	295.7	263.0
Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	483.4	573.0
Total derivative instruments, liabilities	848.9	944.3
Interest rate contracts | Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	6.6	8.8
Total derivative instruments, liabilities	161.2	193.9
Interest rate contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	422.3	508.7
Total derivative instruments, liabilities	290.2	321.4
Foreign exchange contracts | Derivatives designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	99.6	80.0
Total derivative instruments, liabilities	134.5	69.1
Foreign exchange contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	16.2	20.8
Total derivative instruments, liabilities	48.6	40.1
Equity contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	31.8	30.2
Total derivative instruments, liabilities	129.2	131.7
Credit contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, assets	13.1	13.3
Total derivative instruments, liabilities	26.9	35.6
Other contracts | Derivatives not designated as hedging instrument
Derivatives, fair value disclosures
Total derivative instruments, liabilities	$ 354.0	$ 415.5