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, 2020	Dec. 31, 2019
Available-for-sale, Amortized Cost
Amortized Cost	$ 62,741,533	$ 61,970,744
Available-for-sale, Fair Value
Total	67,160,250	64,746,076
Held-to-maturity, Fair Value
Fair Value	2,947,350	3,025,790
Fixed maturities
Available-for-sale, Amortized Cost
Due in one year or less	2,208,672
Due after one year through five years	11,090,362
Due after five years through ten years	14,580,642
Due after ten years	33,823,888
Amortized Cost	61,703,564	60,741,093
Available-for-sale, Fair Value
Due in one year or less	2,206,490
Due after one year through five years	11,494,899
Due after five years through ten years	15,561,473
Due after ten years	36,859,419
Total	66,122,281	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	2,728,529
Amortized Cost	2,728,529	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	2,947,350
Fair Value	$ 2,947,350	$ 3,025,790