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, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Pre-tax Income Taxes and Revenue [Line Items]
Expected tax provision (benefit)	$ (6)	$ 19	$ 16	$ 50
Tax-exempt interest	(4)	(5)	(12)	(13)
Change in liability for uncertain tax positions	0	(17)	0	(17)
Effect of provision to tax return filing adjustment	(4)	(7)	(4)	(7)
State taxes, net of federal benefit	(2)	1	5	2
Foreign taxes	4	(4)	6	3
Taxes on reinsurance	(4)	4	(1)	3
Other	1	(1)	(2)	(1)
Total provision (benefit) for income taxes	$ (15)	$ (10)	$ 8	$ 20
Effective tax rate	(313.30%)	(12.00%)	6.00%	8.40%
Income (loss) before income taxes and equity in earnings of investees	$ (18)	$ 72	$ 79	$ 236
Pretax income (loss)	5	79	145	239
Revenue	212	268	585	736
United States
Pre-tax Income Taxes and Revenue [Line Items]
Income (loss) before income taxes and equity in earnings of investees	(10)	72	92	244
Revenue	181	200	465	606
Bermuda
Pre-tax Income Taxes and Revenue [Line Items]
Income (loss) before income taxes and equity in earnings of investees	31	(14)	67	1
Revenue	32	35	90	94
U.K.
Pre-tax Income Taxes and Revenue [Line Items]
Income (loss) before income taxes and equity in earnings of investees	(13)	21	(9)	(3)
Revenue	(1)	29	29	30
Other
Pre-tax Income Taxes and Revenue [Line Items]
Income (loss) before income taxes and equity in earnings of investees	(3)	0	(5)	(3)
Revenue	$ 0	$ 4	$ 1	$ 6