Investments - Limited Partnership Investments (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Net Investment Income [Line Items]
Investment, Type [Extensible Enumeration]	Partnership Interest [Member]		Partnership Interest [Member]
Fair Value Measured at Net Asset Value Per Share
Net Investment Income [Line Items]
Alternative investments	$ 278		$ 251
Unfunded additional commitments	164
Net gains from limited partnership investments	$ 27	$ 20

Indicates type of investment. Includes, but is not limited to, common stock, preferred stock, convertible security, fixed income security, government security, option purchased, warrant, loan participation and assignment, commercial paper, bankers' acceptance, certificates of deposit, short-term security, repurchase agreement, and other investment company.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 210
-Name Accounting Standards Codification
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480524/946-210-50-6

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
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-Section S99
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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-Topic 946
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
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-Name Accounting Standards Codification
-Section S99
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-Subparagraph (SX 210.12-12A(Column C)(Footnote 4))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480032/946-320-S99-2

+ Details