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	Mar. 31, 2017	Dec. 31, 2016
Held-to-maturity, Fair Value
Fair Value	$ 2,746,375	$ 2,733,340
Fixed maturities
Available-for-sale, Amortized Cost
Due in one year or less	581,578
Due after one year through five years	6,517,012
Due after five years through ten years	7,697,777
Due after ten years	22,248,367
Total	37,044,734
Available-for-sale, Fair Value
Due in one year or less	582,465
Due after one year through five years	6,516,520
Due after five years through ten years	7,618,850
Due after ten years	21,021,978
Total	35,739,813
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	2,758,137
Amortized Cost	2,758,137	2,770,177
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	2,746,375
Fair Value	$ 2,746,375	$ 2,733,340