Certain Long-Duration Contracts With Guarantees (Separate Account Investment Options) (Details) - Annuity Contracts - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Account Investment Options	$ 124,084,371	$ 140,310,565
Equity funds
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Account Investment Options	69,686,791	83,556,771
Bond funds
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Account Investment Options	51,855,361	53,027,241
Money market funds
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Account Investment Options	$ 2,542,219	$ 3,726,553