Allowance for Expected Credit Losses (Details) - Changes in the Allowance for Estimated Uncollectible Reinsurance - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2018	Jan. 01, 2020
Reinsurance recoverables, allowance for uncollectible reinsurance
Reinsurance recoverables (net of allowance for estimated uncollectible reinsurance), balance, beginning of period	$ 8,235
Reinsurance recoverables (net of allowance for estimated uncollectible reinsurance), balance, end of period	8,350
Reinsurance recoverables, allowance for uncollectible reinsurance [Roll Forward]
Reinsurance recoverables, allowance for uncollectible reinsurance, beginning balance	92
Reinsurance recoverables, allowance for estimated uncollectible reinsurance	$ 146
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201601Member
Current period change for estimated uncollectible reinsurance	$ 1
Write-offs of uncollectible reinsurance recoverables	0
Reinsurance recoverables, allowance for uncollectible reinsurance, ending balance	146
Cumulative Effect, Period of Adoption, Adjustment [Member]
Reinsurance recoverables, allowance for uncollectible reinsurance [Roll Forward]
Reinsurance recoverables, allowance for uncollectible reinsurance, beginning balance	53
Reinsurance recoverables, allowance for estimated uncollectible reinsurance	$ 53		$ 53