Securities purchased under an agreement to sell (Details) (USD $) In Millions, unless otherwise specified			3 Months Ended		6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2014 Reverse repurchase agreements	Jun. 30, 2013 Reverse repurchase agreements	Jun. 30, 2014 Reverse repurchase agreements	Jun. 30, 2013 Reverse repurchase agreements	Jun. 30, 2014 Minimum	Jun. 30, 2014 Maximum
Investment Holdings [Line Items]
Reverse repurchase agreements outstanding	$ 33.9	$ 38.1
Securities received as collateral	33.2	37.6
Foreign currency gain (loss)			$ (0.20)	$ 0.50	$ (0.20)	$ 0.04
Maturity term for reverse repurchase agreements							30 days	90 days