Derivatives (Credit Derivatives) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2025	Dec. 31, 2024
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 11	$ 19
Maximum Amount of Future Payments under Credit Default Swaps	$ 478	$ 780
Weighted Average Years to Maturity (2)	4 years 3 months 18 days	4 years 4 months 24 days
Credit default swaps | Aaa/Aa/A
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 2	$ 2
Maximum Amount of Future Payments under Credit Default Swaps	$ 100	$ 100
Weighted Average Years to Maturity (2)	2 years	2 years 8 months 12 days
Credit default swaps | Baa
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 8	$ 7
Maximum Amount of Future Payments under Credit Default Swaps	$ 350	$ 300
Weighted Average Years to Maturity (2)	5 years 2 months 12 days	4 years 6 months
Credit default swaps | Ba
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 1	$ 10
Maximum Amount of Future Payments under Credit Default Swaps	$ 24	$ 376
Weighted Average Years to Maturity (2)	1 year 2 months 12 days	4 years 9 months 18 days
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)	2 months 12 days	1 year