INVESTMENT OPERATIONS - Schedule of Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Fixed Maturities, by Expected Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Available-for-sale, Amortized Cost
Amortized Cost	$ 61,985,929	$ 52,826,470
Available-for-sale, Fair Value
Fair Value	63,347,339	50,264,864
Held-to-maturity, Fair Value
Fair Value	2,640,827	2,547,210
Fixed maturities
Available-for-sale, Amortized Cost
Due in one year or less	1,440,860
Due after one year through five years	10,103,874
Due after five years through ten years	13,210,907
Due after ten years	36,091,357
Amortized Cost	60,846,998
Available-for-sale, Fair Value
Due in one year or less	1,438,699
Due after one year through five years	10,229,353
Due after five years through ten years	13,623,029
Due after ten years	36,917,327
Fair Value	62,208,408
Held-to-maturity, Amortized Cost
Due in one year or less	0
Due after one year through five years	0
Due after five years through ten years	0
Due after ten years	2,576,216
Amortized Cost	2,576,216	2,633,474
Held-to-maturity, Fair Value
Due in one year or less	0
Due after one year through five years	0
Due after five years through ten years	0
Due after ten years	2,640,827
Fair Value	$ 2,640,827	$ 2,547,210