Investments - Strategic Investment in Fortitude Re Narrative (Details) - USD ($)				1 Months Ended	12 Months Ended
	Jan. 01, 2024	Jun. 30, 2020	Nov. 13, 2018	May 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Payments to acquire equity method investments					$ 0	$ 393,800,000	$ 0
Investment					2,443,600,000	1,765,800,000
Fortitude Holdings
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			$ 100,000,000
Transaction costs included in carrying value of investment					17,900,000
Investment					1,200,900,000	460,200,000
Earnings from investment					$ 722,900,000	57,900,000
Ownership percentage					19.90%
Earnings from investment, embedded derivative gains					$ 582,000,000.0	$ 46,200,000
Fortitude Re | Fortitude Holdings
Schedule of Equity Method Investments [Line Items]
Percentage ownership			100.00%
Minimum | Fortitude Re | Fortitude Holdings
Schedule of Equity Method Investments [Line Items]
Assets commitment allocation time limit			30 months
Maximum | Fortitude Re | Fortitude Holdings
Schedule of Equity Method Investments [Line Items]
Assets commitment allocation time limit			36 months
Scenario, Forecast | Fortitude Holdings
Schedule of Equity Method Investments [Line Items]
Purchase price adjustment, payable upon inability to make distribution	$ 20,000,000			$ 80,000,000
Scenario, Forecast | AIG | Affiliated Investment Fund | Fortitude Holdings
Schedule of Equity Method Investments [Line Items]
Ownership percentage acquired		51.60%
Scenario, Forecast | Affiliated Investment Fund | Fortitude Holdings
Schedule of Equity Method Investments [Line Items]
Ownership interest transferred		19.90%
Fortitude Holdings | Scenario, Forecast
Schedule of Equity Method Investments [Line Items]
Ownership interest by parent		71.50%