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	$ 102,596,664	$ 112,844,441
Equity funds
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Account Investment Options	56,191,438	65,755,874
Bond funds
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Account Investment Options	44,794,947	44,672,897
Money market funds
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate Account Investment Options	$ 1,610,279	$ 2,415,670