Schedule V (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2020
Schedule V [Roll Forward]
Reinsurance recoverables, allowance for estimated uncollectible reinsurance	$ 146	$ 92
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member		us-gaap:AccountingStandardsUpdate201601Member
Cumulative Effect, Period of Adoption, Adjustment [Member]
Schedule V [Roll Forward]
Reinsurance recoverables, allowance for estimated uncollectible reinsurance		53		$ 53
Reinsurance recoverables [Member]
Schedule V [Roll Forward]
Valuation and qualifying accounts, balance at beginning of period	$ 92	110	$ 111
Valuation and qualifying accounts, charged to costs and expenses	1	0	0
Valuation and qualifying accounts, charged to other accounts	53	0	0
Valuation and qualifying accounts, deductions	0	18	1
Valuation and qualifying accounts, balance at end of period	146	92	110
Allowance for uncollectible premiums receivable from underwriting activities [Member]
Schedule V [Roll Forward]
Valuation and qualifying accounts, balance at beginning of period	55	54	58
Valuation and qualifying accounts, charged to costs and expenses	95	59	50
Valuation and qualifying accounts, charged to other accounts	2	0	0
Valuation and qualifying accounts, deductions	47	58	54
Valuation and qualifying accounts, balance at end of period	105	55	54
Allowance for uncollectible deductibles [Member]
Schedule V [Roll Forward]
Valuation and qualifying accounts, balance at beginning of period	22	24	26
Valuation and qualifying accounts, charged to costs and expenses	7	(2)	(1)
Valuation and qualifying accounts, charged to other accounts	(2)	0	0
Valuation and qualifying accounts, deductions	0	0	1
Valuation and qualifying accounts, balance at end of period	$ 27	$ 22	$ 24