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	$ 61,861,481	$ 52,452,334
Available-for-sale, Fair Value
Total	64,872,331	49,898,408
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	1,830,025
Due after one year through five years	9,960,533
Due after five years through ten years	13,576,841
Due after ten years	35,548,623
Amortized Cost	60,916,022	51,816,959
Available-for-sale, Fair Value
Due in one year or less	1,828,513
Due after one year through five years	10,147,215
Due after five years through ten years	14,198,510
Due after ten years	37,752,634
Total	63,926,872	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	2,544,054
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