Income Taxes - Effective Tax Rate Reconciliation and Pretax Income (Loss) and Revenue by Tax Jurisdiction (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pre-tax Income Taxes and Revenue [Line Items]
Expected tax provision (benefit)	$ 42	$ 38	$ 31	$ 47
Tax-exempt interest	(4)	(5)	(8)	(10)
Foreign taxes	(1)	4	7	5
Taxes on reinsurance	(1)	3	(1)	4
Other	$ (2)	$ 0	$ 1	$ (2)
Effective tax rate (as a percent)	15.40%	21.90%	18.50%	18.40%
Income (loss) before income taxes	$ 222	$ 181	$ 164	$ 237
Total before tax	222	182	160	240
Revenue	372	266	468	461
United States [Member]
Pre-tax Income Taxes and Revenue [Line Items]
Income (loss) before income taxes	198	190	172	225
Revenue	313	227	406	376
Bermuda [Member]
Pre-tax Income Taxes and Revenue [Line Items]
Income (loss) before income taxes	22	0	15	16
Revenue	45	40	59	73
U.K and Other [Member]
Pre-tax Income Taxes and Revenue [Line Items]
Income (loss) before income taxes	2	(8)	(27)	(1)
Revenue	$ 14	$ (1)	$ 3	$ 12