Derivatives (Credit Derivatives) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Credit Derivatives [Line Items]
Credit Risk Derivatives, at Fair Value, Net	$ 36	$ 11
Maximum Amount of Future Payments under Credit Default Swaps	$ 1,613	$ 1,798
Weighted Average Years to Maturity (2)	4 years 1 month 6 days	3 years 10 months 24 days
Credit Default Swap | Aaa/Aa/A
Credit Derivatives [Line Items]
Credit Risk Derivatives, at Fair Value, Net	$ 11	$ 8
Maximum Amount of Future Payments under Credit Default Swaps	$ 615	$ 689
Weighted Average Years to Maturity (2)	2 years 6 months	2 years
Credit Default Swap | Baa
Credit Derivatives [Line Items]
Credit Risk Derivatives, at Fair Value, Net	$ 25	$ 3
Maximum Amount of Future Payments under Credit Default Swaps	$ 998	$ 1,109
Weighted Average Years to Maturity (2)	5 years 1 month 6 days	5 years