Insurance Liabilities - Discounting of Reserves (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Discounting of Reserves [Line Items]
U.S. workers' compensation	$ 2,261,000,000	$ 2,337,000,000
Retroactive reinsurance	(1,049,000,000)	(1,104,000,000)
Total reserve discount	1,212,000,000	1,233,000,000
Fortitude RE
Discounting of Reserves [Line Items]
Total reserve discount	$ 680,000,000	$ 687,000,000
Discount ceded on sale (as a percent)	100.00%	100.00%
United Kingdom
Discounting of Reserves [Line Items]
Total reserve discount	$ 194,000,000	$ 196,000,000