Recent Acquisitions, Disposals & Other Transactions - Loss Portfolio Transfer - U.S. (Details) - USD ($) $ in Millions	2 Months Ended	3 Months Ended		11 Months Ended	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Nov. 15, 2023	Dec. 31, 2022	Dec. 31, 2021	Nov. 09, 2022	Aug. 08, 2022
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Portfolio transfer reserves cover							$ 746.0	$ 746.0
Additional cover in excess of threshold		$ 275.0			$ 275.0			275.0
Additional cover threshold								821.0
Policy limit								1,096.0
Recognized loss					75.0
Loss portfolio transfer,available		188.6			188.6
Recognized loss related to impaired assets		3.4	$ 34.2
Reserves transferred on closing date							509.0
Cash and investments transferred							$ 630.0
Increase in reinsurance recoverables		509.0
Reduction to cash and investments		630.0
Estimated after-tax expense		100.0
Ceded premiums earned	$ 98.4	$ 121.0		$ 724.9	$ 1,205.3	$ 1,272.7
Deferred gain on ceded premiums reserve	$ 82.4
Minimum
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss corridor retained								75.0
Maximum
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss corridor retained								$ 821.0