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	Sep. 30, 2019	Dec. 31, 2018
Available-for-sale, Amortized Cost
Amortized Cost	$ 62,622,141	$ 52,826,470
Available-for-sale, Fair Value
Fair Value	65,643,018	50,264,864
Held-to-maturity, Fair Value
Fair Value	2,685,076	2,547,210
Fixed maturities
Available-for-sale, Amortized Cost
Due in one year or less	1,831,024
Due after one year through five years	9,983,745
Due after five years through ten years	13,732,775
Due after ten years	35,575,661
Amortized Cost	61,123,205
Available-for-sale, Fair Value
Due in one year or less	1,829,527
Due after one year through five years	10,170,970
Due after five years through ten years	14,362,164
Due after ten years	37,781,421
Fair Value	64,144,082
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	2,544,054
Amortized Cost	2,544,054	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	2,685,076
Fair Value	$ 2,685,076	$ 2,547,210