Investments (Mortgage Loans by Maturity Date) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Loans Receivable, Gross, Commercial, Real Estate	$ 5,861	$ 5,727
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]
Loans Receivable, Gross, Commercial, Real Estate	$ 2,276	$ 1,841
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	38.80%	32.20%
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]
Loans Receivable, Gross, Commercial, Real Estate	$ 2,768	$ 2,944
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	47.30%	51.40%
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]
Loans Receivable, Gross, Commercial, Real Estate	$ 817	$ 942
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	13.90%	16.40%