Investments (Rollforward of expected credit-losses, AFS) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale, Allowance for Credit Loss [Line Items]
Debt Securities, Available for sale, Allowance for Credit Loss	$ 115	$ 168	$ 156	$ 169
Debt Securities, Available-for-sale, Allowance for Credit Loss, Period Increase (Decrease)	31	59
Debt Securities, Available-for-sale, Allowance for Credit Loss, Writeoff	(5)	(2)
Debt Securities, Available-for-sale, Allowance for Credit Loss, Recovery	$ (67)	$ (58)

Amount of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

Amount of increase (decrease) in allowance for credit loss of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 9
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479106/326-30-50-9

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- Definition

Amount of increase in allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), from recovery.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
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-Section 50
-Paragraph 9
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-Publisher FASB
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- Definition

Amount of writeoff of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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