Investments - Narrative (Details) - USD ($)		3 Months Ended	12 Months Ended
	Aug. 06, 2020	Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Debt and Equity Securities, FV-NI [Line Items]
Weighted average duration of debt securities			1 year 7 months 6 days	10 years 6 months
Weighted average duration of debt securities, excluding short-term investments			2 years 3 months 18 days	10 years 6 months
Debt securities		$ 2,085,600,000	$ 2,085,600,000	$ 101,300,000
Other long-term investments		456,100,000	456,100,000	4,000,000.0
Proceeds from redemptions from related party investment funds			200,000,000.0	0	$ 760,000,000.0
Redemption receivable from related party investment fund		250,000,000.0	250,000,000.0	0
Third Point Enhanced LP
Debt and Equity Securities, FV-NI [Line Items]
Eligible withdrawal period after the closing date	5 years
Eligible withdrawal period at each successive anniversary of the closing date	2 years
Eligible withdrawal threshold, percentage of aggregate opening balance and aggregate capital contributions	20.00%
Redemptions from related party investment funds		450,000,000
Proceeds from redemptions from related party investment funds		200,000,000
Redemption receivable from related party investment fund		250,000,000	250,000,000
Investments in related investment party funds, unfunded commitments		0	0
Third Point Venture Offshore Fund I LP
Debt and Equity Securities, FV-NI [Line Items]
Investments in related investment party funds, unfunded commitments		12,700,000	$ 12,700,000
Percentage of net asset value held			16.80%
Hedge funds and private equity funds
Debt and Equity Securities, FV-NI [Line Items]
Other long-term investments		195,700,000	$ 195,700,000	0
Distribution receivable		12,300,000	12,300,000
Investments in related investment party funds, unfunded commitments		26,700,000	26,700,000
AAA
Debt and Equity Securities, FV-NI [Line Items]
Debt securities		696,400,000	696,400,000	53,200,000
AA
Debt and Equity Securities, FV-NI [Line Items]
Debt securities		884,100,000	884,100,000	0
A
Debt and Equity Securities, FV-NI [Line Items]
Debt securities		278,500,000	278,500,000	9,100,000
Sub-prime
Debt and Equity Securities, FV-NI [Line Items]
Debt securities		51,800,000	51,800,000
Sub-prime | AAA
Debt and Equity Securities, FV-NI [Line Items]
Debt securities		35,100,000	35,100,000
Sub-prime | AA
Debt and Equity Securities, FV-NI [Line Items]
Debt securities		16,100,000	16,100,000
Sub-prime | A
Debt and Equity Securities, FV-NI [Line Items]
Debt securities		$ 600,000	$ 600,000	$ 8,700,000