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, 2020	Dec. 31, 2019
Available-for-sale, Amortized Cost
Amortized Cost	$ 62,998,377	$ 61,970,744
Available-for-sale, Fair Value
Total	68,473,565	64,746,076
Held-to-maturity, Fair Value
Fair Value	2,990,170	3,025,790
Fixed maturities
Available-for-sale, Amortized Cost
Due in one year or less	2,067,896
Due after one year through five years	11,455,625
Due after five years through ten years	14,897,323
Due after ten years	33,415,827
Amortized Cost	61,836,671	60,741,093
Available-for-sale, Fair Value
Due in one year or less	2,077,964
Due after one year through five years	11,970,027
Due after five years through ten years	16,103,285
Due after ten years	37,160,583
Total	67,311,859	63,516,425
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	2,680,324
Amortized Cost	2,680,324	2,823,881
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	2,990,170
Fair Value	$ 2,990,170	$ 3,025,790