Derivatives (Credit Derivatives) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 17	$ 36
Maximum Amount of Future Payments under Credit Default Swaps	$ 1,788	$ 1,635
Weighted Average Years to Maturity (2)	4 years	4 years 1 month 6 days
Credit default swaps | Aaa/Aa/A
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 7	$ 11
Maximum Amount of Future Payments under Credit Default Swaps	$ 879	$ 615
Weighted Average Years to Maturity (2)	2 years 9 months 18 days	2 years 6 months
Credit default swaps | Baa
Credit Derivatives [Line Items]
Estimated Fair Value of Credit Default Swaps	$ 10	$ 25
Maximum Amount of Future Payments under Credit Default Swaps	$ 909	$ 1,020
Weighted Average Years to Maturity (2)	5 years 3 months 18 days	5 years 1 month 6 days