Schedule II - Condensed Financial Information of Registrant - Balance Sheets (Details) - USD ($)	Dec. 31, 2021	Feb. 26, 2021	Dec. 31, 2020
Assets
Total investments	$ 4,529,900,000		$ 1,160,900,000
Cash and cash equivalents	999,800,000		526,000,000.0
Amounts due from affiliates	35,600,000
Other assets	126,800,000		18,800,000
Total assets	10,618,300,000		3,535,200,000
Liabilities
Accounts payable, accrued expenses and other liabilities	229,800,000		17,600,000
Amounts due to affiliates	0
Liability-classified capital instruments	87,800,000	$ 137,600,000	0
Debt	816,700,000		114,300,000
Total liabilities	8,115,000,000		1,969,900,000
Shareholders’ equity
Common shares	16,200,000		9,600,000
Additional paid-in capital	1,622,700,000		933,900,000
Retained earnings	665,000,000.0		620,400,000
Accumulated other comprehensive loss	(200,000)		0
Shareholders’ equity attributable to SiriusPoint shareholders	2,503,700,000		1,563,900,000
Total liabilities, noncontrolling interests and shareholders’ equity	10,618,300,000		3,535,200,000
Series B preference shares
Shareholders’ equity
Series B preference shares	200,000,000.0		0
Parent Company
Assets
Total investments	13,000,000.0		4,000,000.0
Cash and cash equivalents	7,900,000		200,000
Investment in subsidiaries	3,405,600,000		1,459,900,000
Amounts due from affiliates	0		96,600,000
Other assets	12,700,000		4,900,000
Total assets	3,439,200,000		1,565,600,000
Liabilities
Accounts payable, accrued expenses and other liabilities	17,400,000		1,700,000
Amounts due to affiliates	13,600,000		0
Liability-classified capital instruments	87,800,000		0
Debt	816,700,000		0
Total liabilities	935,500,000		1,700,000
Shareholders’ equity
Common shares	16,200,000		9,600,000
Additional paid-in capital	1,622,700,000		933,900,000
Retained earnings	665,000,000.0		620,400,000
Accumulated other comprehensive loss	(200,000)		0
Shareholders’ equity attributable to SiriusPoint shareholders	2,503,700,000		1,563,900,000
Total liabilities, noncontrolling interests and shareholders’ equity	3,439,200,000		1,565,600,000
Parent Company | Series B preference shares
Shareholders’ equity
Series B preference shares	$ 200,000,000.0		$ 0