INVESTMENT OPERATIONS - Schedule of Amortized Cost and Fair Value of Investments Classified as Held-to-Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Available-for-sale Amortized Cost
Amortized Cost	$ 52,452,334	$ 39,455,935
Available-for-sale Fair Value
Fair Value	49,898,408	39,488,434
Held-to-maturity, Amortized Cost
Amortized Cost	2,633,474	2,718,904
Held-to-maturity, Fair Value
Fair Value	2,547,210	2,776,327
Fixed Maturities
Available-for-sale Amortized Cost
Due in one year or less	1,121,731
Due after one year through five years	9,255,369
Due after five years through ten years	9,037,543
Due after ten years	32,402,316
Amortized Cost	51,816,959
Available-for-sale Fair Value
Due in one year or less	1,117,140
Due after one year through five years	9,102,884
Due after five years through ten years	8,790,872
Due after ten years	30,252,137
Fair Value	49,263,033
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	2,633,474
Amortized Cost	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	2,547,210
Fair Value	$ 2,547,210	$ 2,776,327