Investments (Mortgage Loans by Credit Quality Indicator) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
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%
Mortgage Loans By Credit Quality Indicator Range Four [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 188	$ 194
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	3.10%	3.40%
Mortgage Loans By Credit Quality Indicator Range Three [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 616	$ 544
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	10.20%	9.50%
Mortgage Loans By Credit Quality Indicator Range Two [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 2,055	$ 1,905
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	33.90%	33.30%
Mortgage Loans By Credit Quality Indicator Range One [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 3,204	$ 3,084
Mortgage Loans On Real Estate Commercial And Consumer Net Percentage Of Total	52.80%	53.80%
Debt Service Coverage Ratio Range Three [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 70	$ 94
Debt Service Coverage Ratio Range Three [Member] | Mortgage Loans By Credit Quality Indicator Range Four [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	26	37
Debt Service Coverage Ratio Range Three [Member] | Mortgage Loans By Credit Quality Indicator Range Three [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	39	39
Debt Service Coverage Ratio Range Three [Member] | Mortgage Loans By Credit Quality Indicator Range Two [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	0	11
Debt Service Coverage Ratio Range Three [Member] | Mortgage Loans By Credit Quality Indicator Range One [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	5	7
Debt Service Coverage Ratio Range Two [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	193	179
Debt Service Coverage Ratio Range Two [Member] | Mortgage Loans By Credit Quality Indicator Range Four [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	61	61
Debt Service Coverage Ratio Range Two [Member] | Mortgage Loans By Credit Quality Indicator Range Three [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	12	13
Debt Service Coverage Ratio Range Two [Member] | Mortgage Loans By Credit Quality Indicator Range Two [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	40	53
Debt Service Coverage Ratio Range Two [Member] | Mortgage Loans By Credit Quality Indicator Range One [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	80	52
Debt Service Coverage Ratio Range One [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	5,800	5,454
Debt Service Coverage Ratio Range One [Member] | Mortgage Loans By Credit Quality Indicator Range Four [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	101	96
Debt Service Coverage Ratio Range One [Member] | Mortgage Loans By Credit Quality Indicator Range Three [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	565	492
Debt Service Coverage Ratio Range One [Member] | Mortgage Loans By Credit Quality Indicator Range Two [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	2,015	1,841
Debt Service Coverage Ratio Range One [Member] | Mortgage Loans By Credit Quality Indicator Range One [Member]
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 3,119	$ 3,025