Investments - Balance Sheet Offsetting, Liabilities (Details) - Derivative liabilities - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Financial Liability Offsetting
Gross amount of recognized liabilities subject to netting agreements	$ 192.8	$ 216.0
Amount of assets that offset the gross amount of liabilities subject to netting agreements not offset in statement of financial position	(100.3)	(88.4)
Collateral pledged, financial liabilities	(77.5)	(118.3)
Net amount of liabilities subject to netting agreements	15.0	9.3
Gross amount of liabilities not subject to netting agreements	$ 576.0	$ 314.5