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	$ 264	$ 228
Maximum Amount of Future Payments under Credit Default Swaps	$ 13,901	$ 12,468
Weighted Average Years to Maturity	4 years	4 years 6 months
Aaa/Aa/A
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 92	$ 82
Maximum Amount of Future Payments under Credit Default Swaps	$ 4,426	$ 3,980
Weighted Average Years to Maturity	2 years 7 months 6 days	2 years 7 months 6 days
Aaa/Aa/A | Single name credit default swaps (3)
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 1	$ 2
Maximum Amount of Future Payments under Credit Default Swaps	$ 140	$ 150
Weighted Average Years to Maturity	1 year 4 months 24 days	1 year 7 months 6 days
Aaa/Aa/A | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 91	$ 80
Maximum Amount of Future Payments under Credit Default Swaps	$ 4,286	$ 3,830
Weighted Average Years to Maturity	2 years 8 months 12 days	2 years 8 months 12 days
Baa [Member]
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 170	$ 146
Maximum Amount of Future Payments under Credit Default Swaps	$ 9,274	$ 8,287
Weighted Average Years to Maturity	4 years 8 months 12 days	5 years 3 months 18 days
Baa [Member] | Single name credit default swaps (3)
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 1	$ 1
Maximum Amount of Future Payments under Credit Default Swaps	$ 99	$ 99
Weighted Average Years to Maturity	1 year 9 months 18 days	2 years 1 month 6 days
Baa [Member] | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 169	$ 145
Maximum Amount of Future Payments under Credit Default Swaps	$ 9,175	$ 8,188
Weighted Average Years to Maturity	4 years 8 months 12 days	5 years 4 months 24 days
B
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 2	$ 2
Maximum Amount of Future Payments under Credit Default Swaps	$ 129	$ 129
Weighted Average Years to Maturity	4 years 8 months 12 days	5 years
B | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 2	$ 2
Maximum Amount of Future Payments under Credit Default Swaps	$ 129	$ 129
Weighted Average Years to Maturity	4 years 8 months 12 days	5 years
Caa
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ (2)	$ (4)
Maximum Amount of Future Payments under Credit Default Swaps	$ 30	$ 30
Weighted Average Years to Maturity	2 years 2 months 12 days	2 years 6 months
Caa | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps		$ (4)
Estimated Fair Value of Credit Default Swaps	$ (2)
Maximum Amount of Future Payments under Credit Default Swaps	$ 30	$ 30
Weighted Average Years to Maturity	2 years 2 months 12 days	2 years 6 months
Ba
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 2	$ 2
Maximum Amount of Future Payments under Credit Default Swaps	$ 42	$ 42
Weighted Average Years to Maturity	2 years 4 months 24 days	2 years 7 months 6 days
Ba | Single name credit default swaps (3)
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 0	$ 0
Maximum Amount of Future Payments under Credit Default Swaps	$ 17	$ 17
Weighted Average Years to Maturity	1 year 10 months 24 days	2 years 1 month 6 days
Ba | Credit default swaps referencing indices
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 2	$ 2
Maximum Amount of Future Payments under Credit Default Swaps	$ 25	$ 25
Weighted Average Years to Maturity	2 years 8 months 12 days	3 years