Income Taxes - Effective Tax Rate Reconciliation and Pretax Income (Loss) and Revenue by Tax Jurisdiction (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Pre-tax Income Taxes and Revenue [Line Items]
Expected tax provision (benefit)	$ (11)	$ 9
Tax-exempt interest	(4)	(5)
State tax	1	1
Foreign taxes	8	1
Taxes on reinsurance	0	1
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Deferred Compensation, Amount	2	(2)
Other	0	(1)
Provision (benefit) for income taxes	$ (4)	$ 4
Effective tax rate (as a percent)	7.10%	7.80%
Income (loss) before income taxes	$ (58)	$ 56
Total before tax	(62)	58
Revenue	96	195
United States [Member]
Pre-tax Income Taxes and Revenue [Line Items]
Income (loss) before income taxes	(26)	35
Revenue	93	149
Bermuda [Member]
Pre-tax Income Taxes and Revenue [Line Items]
Income (loss) before income taxes	(7)	16
Revenue	14	33
U.K and Other [Member]
Pre-tax Income Taxes and Revenue [Line Items]
Income (loss) before income taxes	(29)	7
Revenue	$ (11)	$ 13