Investments (Mortgage Loans by Maturity Date) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Document Period End Date	Mar. 31, 2020
Financing Receivable, before Allowance for Credit Loss	$ 6,063	$ 5,727
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	100.00%	100.00%
Due within five years
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 2,011	$ 1,841
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	33.20%	32.20%
Due after five years through ten years
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 3,107	$ 2,944
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	51.20%	51.40%
Due after ten years
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 945	$ 942
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	15.60%	16.40%