Income Taxes - Effective Tax Rate Reconciliation and Pretax Income (Loss) and Revenue by Tax Jurisdiction (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pre-tax Income Taxes and Revenue [Line Items]
Expected tax provision (benefit) at statutory rates in taxable jurisdictions	$ 9	$ 35
Tax-exempt interest	(5)	(6)
Change in liability for uncertain tax positions	0	(7)
State taxes	1	2
Foreign taxes	1	(4)
Taxes on reinsurance	1	0
Deferred compensation	(2)	(1)
Other	(1)	1
Provision (benefit) for income taxes	$ 4	$ 20
Effective tax rate (as a percent)	7.80%	9.30%
Income (loss) before income taxes	$ 56	$ 217
Total before tax	58	217
Revenue	195	293
United States [Member]
Pre-tax Income Taxes and Revenue [Line Items]
Income (loss) before income taxes	35	175
Revenue	149	247
Bermuda [Member]
Pre-tax Income Taxes and Revenue [Line Items]
Income (loss) before income taxes	16	49
Revenue	33	52
U.K and Other [Member]
Pre-tax Income Taxes and Revenue [Line Items]
Income (loss) before income taxes	7	(7)
Revenue	$ 13	$ (6)