Investments - Equity securities and other-long term investments at fair value (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Debt and Equity Securities, FV-NI [Line Items]
Equity securities	$ 2.8	$ 0.0
Other long-term investments	456.1	4.0
Valued at Level 3
Debt and Equity Securities, FV-NI [Line Items]
Equity securities	0.0
Other long-term investments	336.9	4.0
Fixed income mutual funds
Debt and Equity Securities, FV-NI [Line Items]
Equity securities	2.1
Fixed income mutual funds | Valued at Level 3
Debt and Equity Securities, FV-NI [Line Items]
Equity securities	0.0
Common stocks
Debt and Equity Securities, FV-NI [Line Items]
Equity securities	0.7
Common stocks | Valued at Level 3
Debt and Equity Securities, FV-NI [Line Items]
Equity securities	0.0
Hedge funds and private equity funds
Debt and Equity Securities, FV-NI [Line Items]
Other long-term investments	195.7	0.0
Other long-term investments, unfunded commitments	26.7
Hedge funds and private equity funds | Valued at NAV
Debt and Equity Securities, FV-NI [Line Items]
Other long-term investments	115.2
Hedge funds and private equity funds | Valued at Level 3
Debt and Equity Securities, FV-NI [Line Items]
Other long-term investments	80.5
Strategic Investments and Other Investments
Debt and Equity Securities, FV-NI [Line Items]
Other long-term investments, unfunded commitments	13.8
Strategic Investments
Debt and Equity Securities, FV-NI [Line Items]
Other long-term investments	215.3	4.0
Other investments
Debt and Equity Securities, FV-NI [Line Items]
Other long-term investments	$ 45.1	$ 0.0