Investments - Balance Sheet Offsetting, Assets (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Financial Asset Offsetting
Gross amount of recognized assets subject to netting agreements	$ 526.7	$ 445.4
Amount of liabilities that offset the gross amount of assets subject to netting agreements not offset in statement of financial position	(149.1)	(135.7)
Collateral received, financial assets	(335.9)	(276.3)
Net amount of assets subject to netting agreements	41.7	33.4
Derivative assets
Financial Asset Offsetting
Gross amount of recognized assets subject to netting agreements	386.7	321.0
Amount of liabilities that offset the gross amount of assets subject to netting agreements not offset in statement of financial position	(149.1)	(135.7)
Collateral received, financial assets	(195.6)	(151.9)
Net amount of assets subject to netting agreements	42.0	33.4
Reverse repurchase agreements
Financial Asset Offsetting
Gross amount of recognized assets subject to netting agreements	140.0	124.4
Collateral received, financial assets	(140.3)	$ (124.4)
Net amount of assets subject to netting agreements	$ (0.3)