Investments (Details 16) - Derivative liabilities - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Financial Liability Offsetting
Gross amount of recognized liabilities subject to netting agreements	$ 805.2	$ 786.0
Amount of assets that offset the gross amount of liabilities subject to netting agreements not offset in statement of financial position	(511.6)	(479.5)
Collateral pledged, financial liabilities	(164.5)	(220.6)
Net amount of liabilities subject to netting agreements	129.1	85.9
Gross amount of liabilities not subject to netting agreements	$ 458.7	$ 421.3