Insurance Subsidiary Financial Information and Regulatory Matters - Statutory Accounting Practices Disclosure (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Corbeau Re
Statutory Accounting Practices [Line Items]
Statutory Capital and Surplus (Deficit):	$ 171
Iowa
Statutory Accounting Practices [Line Items]
Statutory Net income (loss):	(462)	$ (243)	$ 351
Statutory Capital and Surplus (Deficit):	2,009	1,877
New York
Statutory Accounting Practices [Line Items]
Statutory Net income (loss):	5	(15)	4
Statutory Capital and Surplus (Deficit):	86	82
Vermont | Raven Re
Statutory Accounting Practices [Line Items]
Statutory Net income (loss):	60	(111)	3
Statutory Capital and Surplus (Deficit):	140	121
Vermont | Corbeau Re
Statutory Accounting Practices [Line Items]
Statutory Net income (loss):	(644)	0	0
Statutory Capital and Surplus (Deficit):		0
Cayman Islands
Statutory Accounting Practices [Line Items]
Statutory Net income (loss):	384	(299)	99
Statutory Capital and Surplus (Deficit):	114	(126)
Bermuda
Statutory Accounting Practices [Line Items]
Statutory Net income (loss):	151	(339)	$ 94
Statutory Capital and Surplus (Deficit):	$ 11	$ (138)