Derivatives (Credit Derivatives) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Credit Derivatives [Line Items]
Credit Risk Derivatives, at Fair Value, Net	$ 41	$ 36
Maximum Amount of Future Payments under Credit Default Swaps	$ 1,755	$ 1,635
Weighted Average Years to Maturity (2)	4 years 3 months 18 days	4 years 1 month 6 days
Credit Default Swap | Aaa/Aa/A
Credit Derivatives [Line Items]
Credit Risk Derivatives, at Fair Value, Net	$ 15	$ 11
Maximum Amount of Future Payments under Credit Default Swaps	$ 683	$ 615
Weighted Average Years to Maturity (2)	2 years 10 months 24 days	2 years 6 months
Credit Default Swap | Baa
Credit Derivatives [Line Items]
Credit Risk Derivatives, at Fair Value, Net	$ 26	$ 25
Maximum Amount of Future Payments under Credit Default Swaps	$ 1,072	$ 1,020
Weighted Average Years to Maturity (2)	5 years 2 months 12 days	5 years 1 month 6 days