Investments - Private equity funds subject to lock-up or commitment periods (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Debt and Equity Securities, FV-NI [Line Items]
Fair value	$ 414.9	$ 456.1
Private equity funds
Debt and Equity Securities, FV-NI [Line Items]
Fair value	73.7	$ 125.4
Private equity funds | 1 - 3 years
Debt and Equity Securities, FV-NI [Line Items]
Fair value	41.5
Private equity funds | 3 – 5 years
Debt and Equity Securities, FV-NI [Line Items]
Fair value	16.0
Private equity funds | 5 – 10 years
Debt and Equity Securities, FV-NI [Line Items]
Fair value	$ 16.2