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	$ 139,147,485	$ 124,084,371
Equity funds
Fair Value, Separate Account Investment [Line Items]
Separate Account Investment Options	82,506,787	69,686,791
Bond funds
Fair Value, Separate Account Investment [Line Items]
Separate Account Investment Options	53,763,563	51,855,361
Money market funds
Fair Value, Separate Account Investment [Line Items]
Separate Account Investment Options	$ 2,877,135	$ 2,542,219