Investments - Strategic Investment in Fortitude Re (Details) - USD ($)				1 Months Ended	3 Months Ended
	Jan. 01, 2024	Jun. 02, 2020	Nov. 13, 2018	May 31, 2020	Jun. 30, 2020	Mar. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Investment						$ 1,936,700,000	$ 1,810,800,000
Cumulative unrealized gains								$ 628,200,000
Fortitude Group Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Ownership percentage acquired			19.90%
Payments to acquire equity method investments			$ 381,000,000
Deferred consideration, maximum			$ 95,000,000
Purchase price adjustment, maximum				$ 99,500,000
Purchase price adjustment, payable upon inability to make distribution				$ 79,600,000
Investment								$ 1,200,900,000
Carlyle FRL
Schedule of Equity Method Investments [Line Items]
Investment						599,900,000
Reversal of investment income					$ 620,700,000
Investment, cost						465,400,000
Fortitude Group Holdings, LLC | Fortitude Re
Schedule of Equity Method Investments [Line Items]
Ownership percentage			100.00%
Carlyle FRL | Fortitude Group Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Ownership percentage acquired		51.60%
Ownership percentage		71.50%
T&D | Fortitude Group Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Ownership percentage acquired		25.00%
Carlyle FRL and T&D | Fortitude Group Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Ownership percentage		96.50%
Carlyle FRL | Fortitude Group Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Ownership interest transferred		19.90%
AIG | Fortitude Group Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Purchase price adjustment, adverse reserve developments, maximum		$ 500,000,000
Minimum | Fortitude Group Holdings, LLC | Fortitude Group Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Assets commitment allocation time limit			30 months
Maximum | Fortitude Group Holdings, LLC | Fortitude Group Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Assets commitment allocation time limit			36 months
Maximum | Fortitude Re | Fortitude Group Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Committed capital						$ 4,700,000,000
Forecast | Fortitude Group Holdings, LLC
Schedule of Equity Method Investments [Line Items]
Purchase price adjustment, payable upon inability to make distribution	$ 19,900,000