Certain Long-Duration Contracts With Guarantees (Separate Account Investment Options) (Details) - Annuity Contracts - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Separate Account Investment [Line Items]
Separate Account Investment Options	$ 117,887,885	$ 102,596,664
Equity funds
Fair Value, Separate Account Investment [Line Items]
Separate Account Investment Options	67,526,437	56,191,438
Bond funds
Fair Value, Separate Account Investment [Line Items]
Separate Account Investment Options	48,484,071	44,794,947
Money market funds
Fair Value, Separate Account Investment [Line Items]
Separate Account Investment Options	$ 1,877,377	$ 1,610,279