Income Taxes - Deferred tax assets (liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred Tax Assets
Loss reserves and tax discount	$ 312	$ 214
Unearned premium reserve and other underwriting related reserves	384	385
Investment-related items	125	130
Employee benefits	282	287
Net operating loss carryover	11	84
Other	34	27
Total Deferred Tax Assets	1,148	1,127
Deferred Tax Assets, Valuation Allowance	(4)	(4)
Deferred Tax Assets, Net of Valuation Allowance	1,144	1,123
Deferred Tax Liabilities
Deferred acquisition costs	(120)	(143)
Net unrealized gains on investments	(758)	(458)
Other depreciable and amortizable assets	(220)	(223)
Total Deferred Tax Liabilities	(1,098)	(824)
Net Deferred Tax Asset	$ 46	$ 299