Reinsurance (Effect of Reinsurance on Net Premiums and Claims and Other Policy Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Policyholder Benefits and Claims Incurred, Net [Abstract]
Claims and other policy benefits	$ 13,872.0	$ 11,982.0	$ 11,673.0
Premiums Earned, Net [Abstract]
Direct Premiums Earned	1,477.0	26.0	33.0
Assumed Premiums Earned	14,281.0	13,830.0	13,354.0
Ceded Premiums Earned	(673.0)	(778.0)	(874.0)
Net premiums	15,085.0	13,078.0	12,513.0
Life Insurance Product Line [Member]
Policyholder Benefits and Claims Incurred, Net [Abstract]
Policyholder Benefits and Claims Incurred, Direct	1,577.0	73.0	59.0
Policyholder Benefits and Claims Incurred, Assumed	12,912.0	12,867.0	12,944.0
Policyholder Benefits and Claims Incurred, Ceded	(679.0)	(667.0)	(763.0)
Claims and other policy benefits	$ 13,810.0	$ 12,273.0	$ 12,240.0

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.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
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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.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
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Amount of reduction of provision for policy benefits and costs incurred for policies ceded.

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