Investments (Mortgage Loans by Maturity Date) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 5,727	$ 4,983
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	100.00%	100.00%
Mortgage Loans On Real Estate Due One Year Through Five Years [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 1,841	$ 1,426
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	32.20%	28.60%
Mortgage Loans On Real Estate Due After Five Years [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 2,944	$ 2,686
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	51.40%	53.90%
Mortgage Loans On Real Estate Due After Ten Years [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 942	$ 871
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	16.40%	17.50%