Derivatives (Credit Derivatives) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2024	Dec. 31, 2023
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 29	$ 27
Maximum Amount of Future Payments under Credit Default Swaps	$ 1,405	$ 1,405
Weighted Average Years to Maturity (2)	3 years 9 months 18 days	3 years 10 months 24 days
Credit default swaps \| Aaa/Aa/A
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 5	$ 6
Maximum Amount of Future Payments under Credit Default Swaps	$ 425	$ 419
Weighted Average Years to Maturity (2)	1 year 4 months 24 days	1 year 7 months 6 days
Credit default swaps \| Baa
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 22	$ 19
Maximum Amount of Future Payments under Credit Default Swaps	$ 952	$ 958
Weighted Average Years to Maturity (2)	4 years 10 months 24 days	4 years 10 months 24 days
Credit default swaps \| Ba
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 2	$ 2
Maximum Amount of Future Payments under Credit Default Swaps	$ 24	$ 24
Weighted Average Years to Maturity (2)	2 years 8 months 12 days	3 years
Credit default swaps \| Caa and Lower
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 0	$ 0
Maximum Amount of Future Payments under Credit Default Swaps	$ 4	$ 4
Weighted Average Years to Maturity (2)	1 year 8 months 12 days	2 years

Maximum potential amount of future undiscounted payments that could be required under the credit derivative, before reduction for potential recoveries under recourse or collateralization provisions.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4K
-Subparagraph (b)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-4K

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Fair value of credit risk derivative asset after deduction of credit risk derivative liability.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 4K
-Subparagraph (c)
-SubTopic 10
-Topic 815
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-4K

+ Details

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Period Type:	instant

- Definition

Average remaining period until maturity of the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	na
Period Type:	duration

- Details

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- Details

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- Details

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- Details

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- Details

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