Allowance for Expected Credit Losses (Details) - Changes in the Allowance for Estimated Uncollectible Reinsurance - USD ($) $ in Millions		3 Months Ended		6 Months Ended
	Dec. 31, 2019	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Reinsurance recoverables, allowance for uncollectible reinsurance
Reinsurance recoverables (net of allowance for estimated uncollectible reinsurance), balance, beginning of period		$ 8,345	$ 8,152	$ 8,350	$ 8,235
Reinsurance recoverables (net of allowance for estimated uncollectible reinsurance), balance, end of period	$ 8,235	8,209	8,093	8,209	8,093
Reinsurance recoverables, allowance for uncollectible reinsurance [Roll Forward]
Reinsurance recoverables, allowance for uncollectible reinsurance, beginning balance		142	149	146	92
Reinsurance recoverables, allowance for estimated uncollectible reinsurance	$ 92	135	156	135	156
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Current period change for estimated uncollectible reinsurance		(7)	7	(11)	11
Write-offs of uncollectible reinsurance recoverables		0	0	0	0
Reinsurance recoverables, allowance for uncollectible reinsurance, ending balance	$ 92	$ 135	$ 156	$ 135	156
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