Recent Acquisitions, Disposals & Other Transactions - Loss Portfolio Transfer - U.S. (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2022	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	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	$ 121.0		$ 1,205.3	$ 1,272.7	$ 1,388.6
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