DERIVATIVE FINANCIAL INSTRUMENTS - Nature and Accounting Treatment of Derivative Financial Instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Derivative asset, fair value	$ 545,645	$ 542,243
Embedded derivative - Modco reinsurance treaties
Derivative [Line Items]
Derivative asset, fair value	616	2,573
Embedded derivative - GLWB
Derivative [Line Items]
Derivative asset, fair value	132,812	121,752
Designated as hedging instrument | Cash flow hedges | Foreign currency swaps
Derivative [Line Items]
Derivative asset, notional amount	0	117,178
Derivative asset, fair value	0	132
Derivative liability, notional amount	117,178	0
Derivative liability, fair value	485	0
Derivatives not designated as hedging instruments
Derivative [Line Items]
Derivative asset, notional amount	11,849,914	11,184,348
Derivative asset, fair value	545,645	542,243
Derivative liability, notional amount	15,102,525	14,274,589
Derivative liability, fair value	802,493	748,821
Derivatives not designated as hedging instruments | Interest rate swaps
Derivative [Line Items]
Derivative asset, notional amount	1,040,000	1,135,000
Derivative asset, fair value	43,730	71,644
Derivative liability, notional amount	822,500	575,000
Derivative liability, fair value	1,953	10,208
Derivatives not designated as hedging instruments | Embedded derivative - Modco reinsurance treaties
Derivative [Line Items]
Derivative asset, notional amount	64,310	64,123
Derivative asset, fair value	616	2,573
Derivative liability, notional amount	2,437,200	2,450,692
Derivative liability, fair value	150,924	141,301
Derivatives not designated as hedging instruments | Embedded derivative - GLWB
Derivative [Line Items]
Derivative asset, notional amount	4,917,362	4,601,633
Derivative asset, fair value	132,812	121,752
Derivative liability, notional amount	5,625,350	5,962,044
Derivative liability, fair value	214,550	237,122
Derivatives not designated as hedging instruments | Embedded derivative - FIA
Derivative [Line Items]
Derivative liability, notional amount	1,610,708	1,496,346
Derivative liability, fair value	170,215	147,368
Derivatives not designated as hedging instruments | Embedded derivative - IUL
Derivative [Line Items]
Derivative liability, notional amount	120,218	103,838
Derivative liability, fair value	51,385	46,051
Derivatives not designated as hedging instruments | Interest Rate Futures
Derivative [Line Items]
Derivative asset, notional amount	698,352	102,587
Derivative asset, fair value	1,917	894
Derivative liability, notional amount	769,621	993,842
Derivative liability, fair value	922	6,611
Derivatives not designated as hedging instruments | Equity futures
Derivative [Line Items]
Derivative asset, notional amount	445,702	654,113
Derivative asset, fair value	1,769	5,805
Derivative liability, notional amount	280,278	102,667
Derivative liability, fair value	3,987	2,907
Derivatives not designated as hedging instruments | Currency futures
Derivative [Line Items]
Derivative asset, notional amount	0	340,058
Derivative asset, fair value	0	7,883
Derivative liability, notional amount	298,852	0
Derivative liability, fair value	6,234	0
Derivatives not designated as hedging instruments | Equity options
Derivative [Line Items]
Derivative asset, notional amount	4,459,031	3,944,444
Derivative asset, fair value	363,614	328,908
Derivative liability, notional amount	3,020,620	2,590,160
Derivative liability, fair value	201,838	157,253
Derivatives not designated as hedging instruments | Interest rate swaptions
Derivative [Line Items]
Derivative asset, notional amount	225,000	225,000
Derivative asset, fair value	1,034	2,503
Derivatives not designated as hedging instruments | Other derivatives
Derivative [Line Items]
Derivative asset, notional amount	157	212
Derivative asset, fair value	$ 153	$ 149