Investments - Balance Sheet Offsetting, Assets (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Financial Asset Offsetting
Gross amount of recognized assets subject to netting agreements	$ 398.1	$ 353.5
Amount of liabilities that offset the gross amount of assets subject to netting agreements not offset in statement of financial position	(133.5)	(100.1)
Collateral received, financial assets	(249.7)	(246.1)
Net amount of assets subject to netting agreements	14.9	7.3
Derivative assets
Financial Asset Offsetting
Gross amount of recognized assets subject to netting agreements	373.0	337.1
Amount of liabilities that offset the gross amount of assets subject to netting agreements not offset in statement of financial position	(133.5)	(100.1)
Collateral received, financial assets	(224.6)	(229.7)
Net amount of assets subject to netting agreements	14.9	7.3
Reverse repurchase agreements
Financial Asset Offsetting
Gross amount of recognized assets subject to netting agreements	25.1	16.4
Collateral received, financial assets	$ (25.1)	$ (16.4)