Investments (Details 15) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Financial Asset Offsetting
Gross amount of recognized assets subject to netting agreements	$ 651.7	$ 716.7
Amount of liabilities that offset the gross amount of assets subject to netting agreements not offset in statement of financial position	(510.5)	(581.5)
Collateral received, financial assets	(128.4)	(133.9)
Net amount of assets subject to netting agreements	12.8	1.3
Derivative assets
Financial Asset Offsetting
Gross amount of recognized assets subject to netting agreements	607.9	664.9
Amount of liabilities that offset the gross amount of assets subject to netting agreements not offset in statement of financial position	(510.5)	(581.5)
Collateral received, financial assets	(84.6)	(82.1)
Net amount of assets subject to netting agreements	12.8	1.3
Gross amount of assets not subject to netting agreements	0.1	0.2
Reverse repurchase agreements
Financial Asset Offsetting
Gross amount of recognized assets subject to netting agreements	43.8	51.8
Collateral received, financial assets	$ (43.8)	$ (51.8)