Allowance for Expected Credit Losses (Details) - Changes in the Allowance for Estimated Uncollectible Reinsurance - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Dec. 31, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Reinsurance recoverables, allowance for uncollectible reinsurance
Reinsurance recoverables (net of allowance for estimated uncollectible reinsurance), balance, beginning of period		$ 8,209	$ 8,093	$ 8,350	$ 8,235
Reinsurance recoverables (net of allowance for estimated uncollectible reinsurance), balance, end of period	$ 8,235	8,329	8,317	8,329	8,317
Reinsurance recoverables, allowance for uncollectible reinsurance [Roll Forward]
Reinsurance recoverables, allowance for uncollectible reinsurance, beginning balance		135	156	146	92
Reinsurance recoverables, allowance for estimated uncollectible reinsurance	$ 92	142	140	142	140
Accounting Standards Update [Extensible List]	Accounting Standards Update 2016-13 [Member]
Current period change for estimated uncollectible reinsurance		7	(16)	(4)	(5)
Write-offs of uncollectible reinsurance recoverables		0	0	0	0
Reinsurance recoverables, allowance for uncollectible reinsurance, ending balance	$ 92	$ 142	$ 140	$ 142	140
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
Reinsurance recoverables, allowance for uncollectible reinsurance, ending balance	$ 53