Reinsurance - Effects of Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Net Premiums
Direct	$ 99,753	$ 85,670	$ 76,320
Assumed	350	432	492
Ceded	(911)	(772)	(680)
Net premiums	99,192	85,330	76,132
Net Benefit Costs
Direct	86,738	71,357	64,339
Assumed	223	379	398
Ceded	(714)	(663)	(549)
Net benefit costs	$ 86,247	$ 71,073	$ 64,188

Amount of earned premiums assumed from other entities.

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Amount of earned premiums ceded to other entities.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 944
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Amount, before premiums ceded to other entities and premiums assumed by the entity, of premiums earned.

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Amount, before effect of policies assumed or ceded, of expense related to provision for policy benefits and costs incurred.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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Amount, after effects of policies assumed or ceded, of expense related to the provision for policy benefits and costs incurred.

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Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums earned.

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Amount of policy benefits and costs incurred for policies assumed.

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Amount of reduction of provision for policy benefits and costs incurred for policies ceded.

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