Income Taxes - Effective Tax Rate Reconciliation and Pretax Income (Loss) and Revenue by Tax Jurisdiction (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Pre-tax Income Taxes and Revenue [Line Items]
Expected tax provision (benefit)	$ 45	$ (6)	$ 88	$ 6
Tax-exempt interest	(3)	(3)	(9)	(10)
NCI	(1)	1	(4)	(5)
Return to provision adjustment	(6)	(20)	(6)	(20)
State taxes	1	2	8	10
Foreign taxes	7	(1)	8	9
Taxes on reinsurance	(1)	0	(1)	(1)
Stock based compensation	2	0	2	4
Other	(1)	0	(2)	1
Total provision (benefit) for income taxes	$ 43	$ (27)	$ 84	$ (6)
Effective tax rate	21.40%	123.50%	18.10%	(12.10%)
Pretax income (loss)	$ 202	$ (22)	$ 466	$ 49
Revenues	403	41	1,046	431
United States
Pre-tax Income Taxes and Revenue [Line Items]
Pretax income (loss)	233	3	458	112
Revenues	373	60	901	435
Bermuda
Pre-tax Income Taxes and Revenue [Line Items]
Pretax income (loss)	(17)	10	41	27
Revenues	30	4	123	43
U.K.
Pre-tax Income Taxes and Revenue [Line Items]
Pretax income (loss)	(10)	(30)	(25)	(75)
Revenues	1	(21)	22	(39)
Other
Pre-tax Income Taxes and Revenue [Line Items]
Pretax income (loss)	(4)	(5)	(8)	(15)
Revenues	$ (1)	$ (2)	$ 0	$ (8)